The Families of the Monocotyledons

COMPARATIVE EMBRYOLOGY OF ANGIOSPERMS is a review of thedevelopmental processes leading to sexual reproduction inflowering plants. On the basis of embryological data andcertain evidences from other areas of study, it lays specialemphasis on the relationship among and within the familiesand orders of angiosperms. Occasionally, inaccuracies inobservation and interpretation are pointed out, alternativeinterpretations offered, gaps in our knowledge highlighted,and prospects outlined. The text is documented with 36tables, 376 figures, and about 5000 literature citations,which contribute to making this book comprehensive. Besidesstudents and research workers interested in angiospermembyology, taxonomists, plant breeders, agriculturists, andhorticulturists will also find much useful information inthis treatise.

Comparative Embryology of Angiosperms

An Analysis of the Flora of Southern Africa: Its Characteristics, Relationships, and Orgins

Hybrid zones are 'natural laboratories' for studying the origin, maintenance and demise of species. Theory predicts that hybrid zones can move in space and time, with significant consequences for both evolutionary and conservation biology, though such movement is often perceived as rare. Here, a review of empirical studies of moving hybrid zones in animals and plants shows 23 examples with observational evidence for movement, and a further 16 where patterns of introgression in molecular markers could be interpreted as signatures of movement. The strengths and weaknesses of methods used for detecting hybrid zone movement are discussed, including long-term replicated sampling, historical surveys, museum/herbarium collections, patterns of relictual populations and introgression of genetic markers into an advancing taxon. Factors governing hybrid zone movement are assessed in the light of the empirical studies, including environmental selection, competition, asymmetric hybridization, dominance drive, hybrid fitness, human activity and climate change. Hybrid zone movement means that untested assumptions of stability in evolutionary studies on hybrid zone can lead to mistaken conclusions. Movement also means that conservation effort aimed at protecting against introgression could unwittingly favour an invading taxon. Moving hybrid zones are of wide interest as examples of evolution in action and possible indicators of environmental change. More long-term experimental studies are needed that incorporate reciprocal transplants, hybridization experiments and surveys of molecular markers and population densities on a range of scales.

/pdf/empirical-study-of-hybrid-zone-movement-x19sitkym4.pdf

Empirical study of hybrid zone movement.

Paleoclimate and evolution, with emphasis on human origins

/pdf/hybridization-and-speciation-in-the-pacific-coast-irises-44cyd34g2a.pdf

Hybridization and Speciation in the Pacific Coast Irises

/pdf/a-revision-of-the-pacific-coast-irises-2jia07dewf.pdf

A Revision of the Pacific Coast Irises

While an interest in the corn cob has been shown by those who have attempted to explain the origin and nature of the ear, the increasing role which the cob is assuming today in industry, in archaeology, and in studies of the origin of maize makes it imperative that a careful comparative study of the cob be undertaken. For many years corn cobs played no special role in the economy of corn production since approximately 90 per cent of the corn produced in the United States was used on the farms for feeding of livestock and most of it was fed as unshelled ears. The cobs remaining from ears that were shelled for poultry feed and the like were often used for fuel. However, with the advent of hybrid corn and large seed-processing plants, cobs have become a major by-product of a rapidly expanding agricultural industry and today ways and means are being sought for their utilization. Of the various uses suggested, one of the most promising is that of a filler in commercially processed feeds. There is some experimental evidence on the feeding value of ground cobs (Gerlaugh and Rogers, 1936), and further experiments are now under way. Other possibilities include its use in the production of furfural or as a substitute for peat-moss. The corn cob plays an even more important role in the hybrid seed-corn industry. Since the grains of corn are produced on the cob, the physical characteristics of that structure affect the handling of the ear during processing. It is known, for instance, that certain corns are more difficult to shell than others, some shatter easily, and in some the grains are removed with difficulty. Some cobs are soft while others are hard and tough; certain cobs are very susceptible to ear-rotting fungi, while others are rarely attacked by these oganisms. Since these differences are of considerable importance to the practical corn-breeder it is necessary that the anatomical, histological, and chemical reasons for these differences be understood. There is another reason why a comparative study of the maize cob is desirable. Both in North and South America archaeologists have excavated a large number of prehistoric sites and have found maize remains in many of these excavations. A few of the best finds have yielded remarkably well-preserved ears, without even a kernel missing, although the ear may have been stored for many centuries. However, at least 90 per cent of the material in archaeological collections is cobs. Since the mature cob is a hard and durable structure and not particularly attrac-

Comparative Histology of the Female Inflorescence of Zea Mays L

In June, 1946, we spent a day searching for fossil plant remains in the late Tertiary deposits in southwestern Idaho. Our primary quest in this region was for petrified evergreen cones that have occasionally turned up, although only in such quantity as to whet the appetite of collectors. The focal point of that day's collecting was approximately 10.5 miles south of Bruneau and .5 mile east of state highway No. 51 which runs-south from Mountain Home, Idaho, through Owyhee County into Nevada. In the course of the day one member of our party, Mr. J. M. Dodds, a County Commissioner, of Boise, discovered a fine specimen of a petrified polypore. More recently, Mr. S. H. Osgood, of Rupert, Idaho, has sent us a fragment of another specimen. Although both of our specimens seem to be clearly referable to -the fossil Fomes idahoensis Brown (Brown, '40), in view of the great rarity of fossil polypores a brief record of the specimens seems worth while. This part of Idaho is well known to local mineral collectors for its abundance of fossil wood, as well as the occasional cones. Most of these fossils are weathering out of a loosely consolidated, fine white sandstone which is overlain by a brownishbuff sandstone of a harder texture likewise yielding petrified plan't remains. Overlying the productive plant beds is a horizon which yields an abundance of wellpreserved, fish jaws (Mylocybrinus robustus Leidy). The only stratigraphical study of the beds in this region is that of Piper's ('24), and the horizon from which our fossils were obtained was apparently in his group No. 8 which is described as "Lake sediments, semi-consolidated, white, gray, and buff sandstones and sandy shales, volcanic ash; ...". These beds have been considered to be of Pliocene age although it is possible that they may be of later origin. In a recent letter (February 20, 1947) Dr. Bobb Schaeffer has informed us of a collection of Mylocyprinus robustus fossil fish pharyngeals in the American Museum that were collected "from an area in southwest Idaho between 'Catherine and Sinker Creeks.' This particular locality is considered to be Pleistocene and as this genus has not previously been reported from older formations I am wondering if your horizon might not also be referable to that period."

Fossil Polypores from Idaho

Yuccas (Yucca, Agavaceae) are an easily recognizable constituent of the vegetation of the International Four Corners; an area made up of portions of Arizona, New Mexico, Sonora and Chihuahua. We recognize three species as native to the region, Yucca baccata, Y. elata and Y. madrensis, together with interspecific hybrids, and document for the first time naturally occurring intersectional hybridization between baccate-fruited (sect. Yucca) and capsular-fruited (sect. Chaenocarpa) species. We examine the reproductive barriers to hybridization operating within the genus, i.e., spatial, temporal and ethological, and we consider circumstances that may have been responsible for the production and widespread distribution of hybrids in the Il-C. These include establishment of syrnpatry, pollinator biology, founding hybrids and human activities. We also reflect on the present situation regarding sexual reproduction in species of Yucca in the Southwest.

/pdf/yuccas-agavaceae-of-the-international-four-corners-27nrcrtb97.pdf

Yuccas (Agavaceae) of the International Four Corners: Southwestern USA and Northwestern Mexico

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