Abstract: The experiments have revealed that (NH4)2SO4 combined with KNO3 at low concentration is of advantage to the formation, growth and differentiation of pollen callus in rice, whereas the high concentration of (NH4)2SO4, whether used separately or in combination with KNO3, obviously inhibits the pollen callus formation. The optimum NH4+ concen- tration is about 7.0 mM (equal to 3.5 mM (NH4)2SO4). A basic medium containing 3.5 mM (NH4)2SO4 and 28 mM KNO3 as nitrogen sources has been established. On such medium the frequency of the pollen callus formation is higher than that on Millers me- dium, and the differentiation of shoot from pollen callus is satisfactory.

Abstract: Recent work concerning the regulation of pollen and pollen tube development at the biochemical level in angiosperms has been reviewed, commencing with the microspore immediately after meiosis and terminating with the entry of the pollen tube into the embryo sac. Some of the topics that have been considered are, (1) the role of the tapetum in pollen development, (2) gene activity in the microspore and pollen grain prior to anthesis, (3) DNA synthesis in the microspore and pollen tube, (4) the types of RNA and protein synthesized in the pollen tube including the biochemistry of the vegetative and generative nuclei and finally, (5) the interactions between pollen and pistil after pollination.

Abstract: GENETICS OF INCOMPATIBILITY SySTEMS 406 .cYTOLOGICAL AND PHYSIOLOGICAL CORRELATES OF SI SySTEMS 408 THE PO LLEN GRAIN IN THE INCOM PATIBI LI TY RESPONSE 408 General Features ..... . � . . . . . . . . . . . . . . 408 The Pollen Wall 409 Emission of Pollen Wall Proteins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Characterization of the Emitted Fractions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 411

Abstract: Pollen of L. longiflorum was grown in 45Ca-labeled medium and washed with nonradioactive medium. Whole, labeled pollen was then frozen and autoradiographed at -78 degrees C. The autoradiographs show striking accumulations of 45Ca in the growing tips of the pollen tubes. This result is obtained when the pollen is labeled for times as short as 1 min, or as long as 5 h. In most cases, the tip concentration is about two to four times greater than that in the bulk of the pollen tube, and extends for a length of about 20 mum. In autoradiographs of tubes longer than 1 mm, a small fraction of cells show a distinctly larger 45Ca accumulation, the tip containing more than 100 times that in the rest of the cell. The 1- to 5-h labeling experiments show that calcium is relatively concentrated within the cytoplasm of the growing tip. The 1- to 3-min labeling experiments suggest that calcium may enter the tip faster than it enters other regions. These patterns of calcium accumulation and flux may be related to the localized secretion of vesicles at the grow;ng tip.

Abstract: Embryogenesis was induced in anthers of two cultivars of B. campestris L. cultured on a modified B5 medium of Gamborg and co-workers (1968). Analysis of mature plants derived from the embryoids revealed the presence of diploids and polyploids. It was, however, demonstrated that the plants were derived from pollen.

Abstract: The pollination mechanisms and pollen vectors of Solanum rostratum have been examined by greenhouse experiments and field studies. Although the capacity for autogamy exists in this weedy annual, it rarely occurs because of two factors: (1) the morphology of the flower and (2) the foraging behavior of the various species of Bombus, the primary pollen vector in the regions studied. The percentages of geitonogamy and xenogamy are dependent on the flight pattern of the bees and the number of open flowers on a plant. CASUAL OBSERVATIONS made on a population of Solanum rostratum Dunal in early June, 1972, in Marshall County, Oklahoma, near the University of Oklahoma Biological Station, suggested that the plants were bumble bee pollinated. This study was undertaken to determine the vector or vectors of pollen transfer, the mechanism of reproduction, and the roles in reproduction, if any, of the large anther and of the projection of the style from the side of the blossom (enantiostyly). MATERIALS AND METHODS-During the summer of 1972 field studies were conducted on a single population of S. rostratum and its floral visitors in Marshall County, Oklahoma (Table 1). These studies were continued in the summer of 1973 on three populations in Cleveland County, Oklahoma, and on greenhouse transplants from two locations in Cleveland County and one in McClain County, Oklahoma. In addition, limited observations were made on two populations in Texas and one in Iowa as comparisons. Floral phenology and morphology were observed and related to pollination and reproduction of the plants. Data collected include time of floral opening and closing, time of anthesis, region of stigmatic receptivity, relative size and position of stamens, and position of the style. Two sets of experiments were conducted to determine the mode of reproduction: (1) Bags were placed over flowers that had been emasculated in bud, over single nontreated flowers, and 'Received for publication 17 July 1974. Acknowledgments: The author wishes to thank J. R. Estes for his valuable assistance throughout the course of this study and especially for his critical reading and suggestions on the manuscript. Sincere appreciation is also expressed to R. W. Thorp for his identifications of the insect visitors and Kathy Kaputska for her illustrations. Submitted in partial fulfillment of the requirements for the degree of Master of Science. 2 Present address: Department of Entomology, Kansas State University, Manhattan, Kansas 66506. over entire inflorescences; seed-set among the treatments was compared. (2) Hand-pollination experiments were undertaken in the greenhouse to examine possible differential fertility of the dimorphic anthers and to test the capability for autogamy, geitonogamy, and xenogamy. Pollen was transferred within a flower, between flowers of one plant, and between flowers of different plants. The results of pollination using the two types of anthers were maintained separately. Seed-set was determined from mature fruits and results compared with that obtained in the field. Pollen from both types of anthers was stained with lactophenol-analine blue and examined for fertility. Over 100 hr were spent observing and recording the frequency, periodicity, and behavior of insect visitation. Insect behavior was observed and recorded with a Mamiya-Sekor 35 mm camera or a Pentax 35 mm camera with a macro lens and with a Cinekodak Special 16 mm movie camera. The movie film was analyzed frame-by-frame with a Vanguard motion analyzer. Insects were collected, identified, and the position, quantity, and composition of pollen loads examined. Insects were tracked in the field (South Base, Lindsey Street, and Lake Thunderbird) over five days to estimate the potential for xenogamy and geitonogamy. Several experiments with fluorescent powder (d -3-5 pm) as a marker were conducted to monitor pollen dispersal: (1) The apices of the small anthers of ten open flowers of one plant (South Base) were marked at 0630 hr CDT; all open flowers in the population were collected in the evening and examined under a ChromatoVue UV viewing cabinet. (2) The apices of the large anthers of 11 open flowers on a greenhousegrown plant were also marked and the plant was placed within the Lake Thunderbird population and observed. All flowers visited by bees subseauent to visitation of the test Dlant were imme-

Abstract: The palaeoecology of six Scottish blanket peat profiles containing pine stumps was investigated by means of peat stratigraphy, pollen analysis, and radiocarbon dating. In addition, several other pine and birch remains from peat in other areas of Scotland were radiocarbon dated. Three peat profiles were selected in each of two contrasting regions. The Cairngorm area is within the distributional area of native pine today and pollen analysis has shown that pine has been a major component of the upland forest since about 7000 b.p. The Galloway region in southwest Scotland is south of the native pine area, and pollen analysis has shown that pine has never been a major component of the upland forest. Despite the limitations of the methods used, it has been established that there were several different circumstances for the growth and death of the pines studied, and that their ages are asynchronous within and between the two areas. Thus little regional climatic significance can be assumed from their occurrence, and they cannot be taken as evidence in support of dry Boreal and sub-Boreal periods in the Blytt and Sernander climatic scheme. In the northwest Highlands dates from pine stumps and major declines of pollen in pollen diagrams are consistently around 4000 b.p. This overall demise of pine may have a regional climatic cause in this area.

Abstract: (p. 34)The use of palynological information from caves, rock-shelters, and prehistoric settlements for the reconstruction of vegetation and climate in the past is a matter requiring great caution, and cannot be done without corrections.In the first place, pollen types of zoogamous plants, especially when present in great numbers, have to be judged critically. Pollen of Liguliflorae and some types of Tubuli florae are by preferenceto be excluded from the pollen sum.When sampling a prehistoric site, great care has to be exercised; the profile has to be cut back and a clear stratigraphy has to be looked out for.One has to consider tbe possibility of infiltration of younger material, contamination with types selected by burrowing bees, transport of building material containing pollen, and (selective) corrosion.

Abstract: Angiosperm pollen grains possess walls of remarkable structural complexity, and the architectural forms encountered are often sufficiently specific and consistent to be useful taxonomically. Lindley, von Mohl and others appreciated this systematic potential almost a century and a half ago, and today a comprehensive pollen taxonomy is taking shape with the publication of the World pollen flora founded by the late Professor Gunnar Erdtman. Surprisingly, until quite recently this interest in the taxonomic aspects of pollen wall morphology has not been matched by any great concern for the functional significance of even the most conspicuous features, such for example as the deep sculpturing so commonly found in the outer layer of the wall. When Erdtman spent a period in my laboratory in Belfast in the mid-1950s we talked at length about pollen and spore morphology and morphogenesis, but I do not recall that we seriously touched upon the adaptive meaning of the wall architecture. We need not have heen so blind, for there were already many suggestive leads. Wodehouse in his distinguished book of 1935 addressed himself not only to the problems of pollen wall morphogenesis, but noted also relations between structure and dispersal agency. German authors had thought along similar lines, and had already pointed to the functional importance of one type of pollen surface material, that which in some species acts as a binding agent ( Polenkitt ), holding grains together in groups and facilitating attachment to pollen vectors. Much earlier had appeared the work of Green (1894), who seems to have been the first to study the nature of pollen emissions. In an early application of substrate film methods, Green showed that intact moistened pollen grains released various hydrolytic enzymes, and surmised that these played some part in the pollen-stigma interaction, perhaps in germination and pollen-tube growth and nutrition. When Green wrote, Blackley’s famous work on the causes of hay fever was already 20 years old; and by the 1950s it was well established that the active constituents released by pollen were non-dialysable and predominantly protein in nature. Various authors commented on the rapidity with which protein exudates are released from pollen grains, and there was speculation on the sources of such mobile fractions; indeed the facts suggested the possibility that these, too, were held like Pollenkitt in sites at or near the surface.

Abstract: Pollen from Lake Annie, Highlands County, south-central Florida, can be divided into three zones. Zone 3, dating from 37,000 to 13,010 B.P., is characterized by pollen of the shrub Ceratiola (rosemary) and Polygonella spp., implying a very dry climate. Zone 2, dating from 13,010 to 4,715 B.P., has abundant pollen of Quercus (oak) and Ambrosia (ragweed), indicating an upland vegetation of oak scrub and prairie. From 4,715 B.P. to the present (zone 1), the modern flora and climate have prevailed.

Abstract: The respiration and vitality of ungerminated bi- and trinucleate pollen were studied in order to determine the influence of relative humidity and temperature on metabolic activity The gas exchange, germination capacity and staining with tetrazolium bromide were followed under standardized conditions A constant respiration rate occurred under conditions of high relative humidity (97%) Per mg pollen, the trinucleate grains of Compositae and Gramineae respired 2 to 3 times as intense as 6 species of binucleate grains Per unit of pollen protein the differences were even larger In contrast to binucleate pollen, the longevity of trinucleate pollen was very short and the ability to germinate was lost twice as fast as the respiration capacity This limits the use of tetrazolium bromide as an indicator of viability At reduced relative humidities respiration was strongly restricted, but the longevity of bi- and trinucleate pollen considerably increased Pollen of Gramineae, however, was very sensitive to changes in relative humidity; short exposure to low relative humidity decreased both the vitality and the capacity to respire

Abstract: SUMMARY Results are presented from Principal Components Analysis of three data matrices (pollen concentration per cc, percentages of total pollen, and analyses for eight or nine chemical elements) of c thirty samples from each of two profiles of lake sediment of Late-Devensian age (15000 to 10000 years BP) from the Lake District and NW Scotland The groupings of samples by their scores on the first two components of these Principal Components Analyses have been shown to produce similar divisions (zonations) to those originally produced subjectively by inspection of the percentage pollen diagrams Though neither profile includes the classical Late-Weichselian oscillation of pollen zones I, II and III, involving expansion of percentages of birch pollen within biogenic sediment between two minerogenic layers, numerical analysis has revealed in the data from both sites a pattern involving a threefold division with revertence, and another pattern of twofold division The subjective zonation of the percentage diagrams clearly involved a process of mental integration of these two patterns A plot of the scores of the samples on the first two components of the Principal Components Analyses groups the samples into clusters corresponding with the zones determined by inspection; similar results are obtained for each of the three Principal Components Analyses This is interpreted as indicative of a close relationship between pollen and chemical data which can most readily be explained on the hypothesis that the boundaries of pollen zones represent the results of environmental changes which simultaneously affected soils and vegetation

Abstract: Fresh pollen of C. bipinnatus was extracted for 45 min in an isotonic mannitol-CaCl$_{2}$ medium that preserved pollen viability. The pollen-wall diffusates after partial purification by ammonium sulphate precipitation and gel filtration contained more than 7 protein bands by polyacrylamide gel electrophoresis. Two fractions contained demonstrable carbohydrate, suggesting they are glycoproteins. After SDS gel electrophoresis, many bands were obtained, the 2 major fractions having estimated (relative) molecular masses of 11 500 and 30 000. Gel patterns of C. bipinnatus pollen diffusate were compared with those from ragweed diffusate and antigen E. The pollen-wall proteins are implicated in the control of self incompatibility. In compatible matings, most pollen tubes had grown through the style to the ovary within 60 min after pollination. After self pollination, the pollen tube is arrested on the stigma surface, and the callose rejection response was detected within 15 min of pollination. Self incompatibility was partially overcome (to ca. 27% of compatible seed set) with pollen mixes of killed compatible and fresh self pollen. These could be replaced with equal effect by applying compatible pollen-wall diffusate (containing 1 mg/ml protein) followed by self pollination. The active proteins are heat stable, and include an antigen E-like fraction with partial immunological identity to the ragweed allergen.

Abstract: Comparative study of pollen of the ranalean complex has revealed a remarkable, hitherto unrecognized characteristic of primitive angiosperm pollen, namely, its complete lack of columellae. Pollen with such exine has been desnated atectate anid taxa in the Magnoliaceae. Degenzeriaceae, Eupomatiaceae, Annonraceae, and possibly Himantandraceae and Nymphaeaceae have pollen which is considered to be primitively columellaless.

Abstract: In order to measure differences in the pollen growth rate of numerous lines of maize and to investigate the main features of their genetic control, gametophyte growth was studied in vitro and in vivo. In vitro pollen tube growth of twenty inbred lines and seven hybrids was measured; a remarkable variability was observed in the growth rate of the inbred lines examined: most lines were distinct, showing different levels of growth. Analysis of frequency distribution of pollen tube lengths for pairs of inbred lines and their F1′ s revealed greater variance among lengths of F1 pollen tubes, presumably indicating the segregation of genetic factors expressed in the gametophyte. Similar frequency distributions of tube lengths in pollen produced by two pairs of reciprocal hybrids virtually excluded the presence of a cytoplasmic component. In vivo competitive ability of pollen tubes was measured as the increase in relative fertilization frequency from apex to base of the ear. Mixtures were made using two types of genetically distinguishable pollen, and were applied to a female common parent. Nine pairs of inbred lines furnished the pollen for the mixtures. In all cases where the B14 line was involved, this pollen type fertilized nearly all the ovules, perhaps indicating the presence of a gametophytic factor. When other lines were compared, the ears contained mixtures of the two possible seed types, the relative proportions of which indicated the differential competitive abilities of the two pollen tube types. A comparison between in vitro and in vivo behavior was made for some genotypes. In vivo results generally agreed with in vitro results. The degree of the differences between lines however was changed, presumably because pollen-style or pollen-pollen interactions are absent in vitro. Differing growth patterns between lines were also revealed in vivo by direct observation of fluorescent pollen tubes within the silks, a finding which may be useful in further studies.

Abstract: Veracruz is physiographically the most diverse state in Mexico, with altitudes ranging from sea level to the highest peak in Mexico (Pico de Orizaba, 5747 m). This diversity in environments is reflected in a complex mosaic of vegetation estimated at 8000-10,000 species. Studies by GomezPompa (1973) have identified the principal plant communities of Veracruz and provide information on their ecology, composition and distribution. Recently paleobotanical data has become available that, with better understanding of present-day vegetation, reveal some trends in the Cenozoic evolution of lowland communities in Veracruz. An assemblage of 110 identified fossil pollen and spores has been recovered from lignites of the Paraje Solo formation near Coatzacoalcos, Veracruz, Mexico (Table 1). The age of the sediments is upper Miocene and the microfossils thus represent remnants of a vegetation occupying lowlands and adjacent slopes of the Sierra Madre Oriental approximately 10-12 million years ago. With the data available on modern vegetation, these fossils may be arranged into paleocommunities and a comparison made between fossil and modern biotas. Some similarities are evident, together with distinct differences, especially with regard to the Tropical Rain Forest, arid lowland vegetation, and communities suspected (but not proven) to result from anthropogenic influences. A summary of upper Miocene and modern vegetation from southeastern Veracruz is presented in Figure 1. The present-day communities are listed along the left and bottom of the chart with three east-west transects shown along the eastern escarpment from about 1700 m elevation to the Gulf Coast (Gomez-Pompa, 1973). Fossil taxa are placed according to known natural occurrences and may appear in more than one paleocommunity. In a few cases pollen of two genera could not consistently be distinguished in the fossil condition (Eugenia/Myrcia, Combretum/Terminalia, Hampea/Hibiscus). An occasional wellpreserved, critically oriented grain has indicated the probable presence of each genus, and all are included in reconstruction of the paleocommunities although estimates of the relative abundance of these taxa are not possible. The Palmae and Gramineae are listed only for palm stands and savannas but pollen of palms and grasses (and Compositae) are found in all samples, and the modern plants occur scattered throughout most types of vegetation in Veracruz. Pollen of the Lauraceae does not fossilize or survive processing techniques. The criteria used to estimate presence or absence and relative importance of various paleocommunities in the Miocene vegetation are a) occurrence of pollen of the dominants, b) presence of genera characteristically associated with a particular vegetation type, as opposed to wide-ranging genera occurring in several types of communities, and c) abundance of each pollen type, with compensation for distance from the depositional basin, differential pollen production, and nature of the pollination mechanisms (to the extent these data are available).

Abstract: The postglacial history of vegetation in the Yale area of the lower Fraser River Canyon is described from sediments of two lakes using percentage pollen analysis supplemented with macrofossil evide...

Abstract: ___________________ Introduction _________________ Previous reports, North American __ Taxonomic reports ________ Nontaxonomic references _____ Acknowledgments ___________ Methods ___________________ Fossil pollen sample localities _______ Type specimens _______________ Systematic descriptions ___________ Genus Basopollis ____________ Basopollis obscurocostatus, n. sp Genus Choanopollenites ________ cf. Choanopollenites sp ______ Genus Complexiopollis _________ Genus Extremipollis __________ Extremipollis vivus, n. sp ____ Extremipollis versatilis, n. sp __ Extremipollis caminus, n. sp __ Genus Interpollis ____________ Interpollis cf. /. supplingensis __ Interpollis microsupplingensis __ Interpollis intranodus, n. sp ___ Genus Interporopollenites _______ __________ 9 -----____ 9 __________ 9 10 ________ 10 __________ 11 __________ 11 12 _________ 12 __________ 12 Interporopollenites turgidus, n. sp __________ 13 Genus Kyandopollenites ___________________ 13 Kyandopollenites anneratus ______________ 13 Genus Megatriopollis ____________________ 13 Megatriopollisl sp ____________________ 14 Genus Minorpollis ______________________ 14 Minorpollis minimus __________________ 14 Minorpollis aff. M. minimus _____________ 14 Genus Nudopollis ______________________ 15 Nudopollis endangulatus ________________ 15 Nudopollis aff. N. endangulatus ___________ 15 Nudopollis terminalis __________________ 15 Nudopollis terminalis subsp. hastaformis ______ 15 Nudopollis terminalis subsp. hebeformis _______ 15 Nudopollis aff. N. terminalis _____________ 16 Nudopollis thiergartii ___________________ 16 Nudopollis thiergartii subsp. rneridium _______ 16 Nudopollis thiergartii subsp. conspicuus _______ 16 Nudopollis thiergartii subsp. minutus ________ 16 Nudopollis aff. N. thiergartii _____________ 16 Genus Pecakipollis ______________________ 16 cf. Pecakipollis sp ____________________ 16 Genus Plicapollis _______________________ 17 Plicapollis usitatus, n. sp _______________ 17 Plicapollis retusus, n. sp ________________ 18 Plicapollis vacuus, n. sp ________________ 18 Page Systematic descriptions Continued Genus Plicapollis Continued Plicapollis rusticus, n. sp _______________ 18 Genus Pompeckjoidaepollenites ______________ 19 Pompeckjoidaepollenites aff. P. subhercynicus ___ 19 Genus Oculopollis ______________________ 20 Genus Pseudoculopollis ___________________ 20 Pseudoculopollis admirabilis, n. sp __________ 20 Pseudoculopollis sp. A _________________ 20 Genus Semioculopollis ____________________ 21 Semioculopollis sp. A __________________ 21 Genus Pseudoplicapollis ___________________ 21 Pseudoplicapollis endocuspis, n. sp __________ 22 Pseudoplicapollis serenus, n. sp ____________ 22 Pseudoplicapollis sp. A_________________ 22 Genus Pseudovacuopollis __________________ 23 Pseudovacuopollis involutus, n. sp __________ 23 Genus Thomsonipollis ____________________ 24 Thomsonipollis magnificus _______________ 24 Thomsonipollis magnificoides _____________ 24 Thomsonipollis aff. T. magnificoides _________ 24 Thomsonipollis expolitus, n. sp ____________ 25 Genus Trudopollis ______________________ 25 Trudopollis variabilis, n. sp _____________ 25 Trudopollis plenus, n. sp ________________ 26 Trudopollis cf. T. artifex ________________ 26 Trudopollis sp. A ____________________ 27 Trudopollis sp. B ____________________ 27 Trudopollis sp. C ____________________ 28 Genus Vacuopollis ______________________ 28 Vacuopollis munitus, n. sp _______________ 28 Genus Osculapollis, n. gen _________________ 29 Osculapollis aequalis, n. sp ______________ 29 Osculapollis perspectus, n. sp _____________ 29 Osculapollis sp. A ____________________ 30 Genus Praecursipollis, n. gen ________________ 30 Praecursipollis plebius, n. sp _____________ 30 Genus Pseudatlantopollis, n. gen ______________ 30 Pseudatlantopollis simulatus, n. sp __________ 31 Genus Endoinfundibulapollis, n. gen ___________ 31 Endoinfundibulapollis distinctus, n. sp _______ 31 New genus A _________________________ 32 New genus B _________________________ 32 New genus C _________________________ 32 New genus D _________________________ 33 Key to Mississippi embayment Normapolles genera _____ 33 Stratigraphic distribution of Normapolles genera _______ 35 Stratigraphic distribution of Normapolles species ______ 37 References _____________________________ 39 Index ______ ____ ____ _____ ____ ___ 41

Abstract: Out of 46 species and 9 interspecific hybrids ofSolanum studied, 17 tuber-bearing species, 2 non-tuber-bearing species and 4 interspecific hybrids ofSolanum produced pollen plants through anther culture. Haploidy was confirmed in 167 plants of 11 species and 2 interspecific hybrids ofSolanum. Plantlets which were formed directly from pollen almost always proved to be haploids, while plantlets which were redifferentiated from pollen-calli gave haploid, diploid, triploid, tetraploid and even aneuploid plants.

Abstract: The growth of the pollen tube wall of Oenothera organensis results from the insertion of bodies, composed principally of fibrils, synthesized in cytoplasm. This material for the early growth of the tube wall is derived from double membraned inclusions, present in the pollen on release from the anther. The wall of the later tube is derived from the products of dictyosome vesicles, believed to be non-cellulosic glucans. Some of these vesicles, which are formed in very large numbers on germination of the pollen grain, form an association with banked complexes of mitochondria, and it is proposed that this association indicates that phosphorylation of glucan precursors occurs within the vesicles, rather than in the dictyosome. The mechanism of tube wall growth following incompatible cross-pollinations is identical with that following compatible crosses. The early incompatible tube, however, contains far lower levels of free carbohydrates. Among these carbohydrates must be the precursors required for glucan synthesis, for the tube wall is laid down only thinly at this stage. Once the incompatible tube has passed through the outer layer of the stigmatic cells and their secretion, growth similar to that of a compatible tube starts. Subsequent growth of the tube appears to depend upon the amount of reserve material that passes through the region of low carbohydrate content. While the early interactions between the pollen and stigma are far from understood, it is clear that the self-incompatibility system acts principally during growth of the tube in the viscous fluid coating the outer stigmatic cells.

Abstract: A dimorphism is observed in barley (Hordeum vulgare L, cv Akka) pollen when stained with acetocarmine from the mid-binucleate stage onwards The majority of grains have staining cytoplasms, while the remainder have cytoplasms which take up little or no stain (NS grains) The staining dimorphism cannot be detected at the late-uninucleate microspore stage when anthers are normally cultured, but the evidence suggests that the microspores have already diverged at this time and it is the cells destined to become NS grains in vivo that respond in culture to become pollen calluses Evidence comes from a comparison of the frequencies of NS grains and pollen calluses and from their distribution between and within anthers

Abstract: The isolated pollen ofNicotiana tabacum cv. “Badischer Burley” obtained from coldtreated anthers (4 °C for 72 hours) cultured for 4 days, have been induced to undergo androgenesis on a synthetic medium enriched with amino acids. The advantages and potential of the culture of isolated pollen for the induction of haploids and mutation work are discussed.

Abstract: Incompatible pollen in this homomorphic species is inhibited on the stigma which suggests that determination of the pollen reaction might be sporophytic. On the other hand, the genetical evidence so far obtained suggests that the reaction of the pollen is under gametophytic control. Furthermore, the pollen is binucleate and callose appears to be laid down inside the grains of incompatible pollen which exhibit a zone of intense fluorescence when viewed under the microscope. The implications of these findings are discussed.