Hydrocharis

Abstract: Plastic responses of 10 aquatic plant species from 5 rivers and 5 lakes in NW Poland were examined. Chara fragilis , C. delicatula , Potamogeton pectinatus , P. perfoliatus , P. natans , Spirodela polyrhiza , Hydrocharis morsus-ranae , Salvinia natans , Nymphoides peltata and Juncus bulbosus were the subject of research. In the running water of rivers, rhizophytes were generally bigger and they allocated from 0.6% to 58.6% more biomass for anchoring in the substrate than in stagnant water (ox bow lakes). In both flow variants rhizophytes allocated a similar biomass fraction for generative reproduction. On the other hand, under the influence of water flow pleustophytes reduced the mass of an individual ( Spirodela by 25%, Hydrocharis 67%, Salvinia 77%) and emergent structures (p<0.001), and the number of sporangia (p<0.001). In both flow variants the input of biomass to generative reproduction was the same ( Salvinia ), or it was greater in running water ( Hydrocharis ; an increase from 4.9±1.3% to 15.1±3.6%). Under the conditions of strong wave action, in comparison with the lack of this environmental factor, Chara delicatula was several times shorter (p<0.001). However, it was also stouter, and as a result it had similar mass. In the areas of wave action the plant allocated 88.8% of its mass for anchoring in the substrate, whereas when there were no waves, only 22.7%.

Abstract: Regular sequences of leaf and bud formation occur in several members of the Hydrocharitaceae, including Hydrocharis, in which buds are normally formed in the axil of every second leaf of the phyllotactic spiral. Leaf inception begins by periclinal divisions of the inner cells of the 2-layered tunica. Bud formation, which occurs in the apical meristem itself, immediately following the inception of the subtending leaf primordium, begins by divisions in various planes in the corpus, the 2 tunica layers remaining continuous throughout. The young bud meristem soon gives rise to a lateral bud, before leaf formation begins upon it. Because of these and other features, this species is one of considerable morphogenetic interest. Morphogenesis of the whole plant, and in particular the factors controlling the regular sequence of leaf and bud formation, have been and are being investigated experimentally. HYDROCHARIS morsus-ranae L. is a floating aquatic plant with a rosette of spirally arranged leaves and numerous pendent adventitious roots. During the summer months, in Europe, the plant produces long, leafless stolons which termillate in a rosette of leaves and themselves give rise to stolons of the second order; this pattern of growth is repeated in successive branches of higher order. A population of Hydrocharis thus consists of a mat of branching plants of some complexity, although, in fact, only a small proportion of the buds present actually form stolons. In autumn, the stolon apices form dormalnt winter buds, or turions, of some size and complexity; these sink to the bottom of the pond or canal and overwinter there. In the following spring the turions rise to the surface and expand to form new plants. The physiology of dormancy in turions, especially the effects of light and temperature, has already been extensively studied (Vegis, 1955), and their behavior on the renewal of growth, in various conditions, has been examined by the writer as a contributioni to whole-plant morphogenesis. The results will be reported in later papers. Although the morphology of Hydrocharis and related genera was closely examined some 60-100 years ago, these materials are still of considerable interest to students of morphogenesis. For example, as the earlier workers reported, in Hydrocharis buds are formed only in the axil of every second leaf of the rosette (Irmisch, 1859, 1865; Rohrbach, 1873). This observation, which has been confirmed in a short contemporary paper by Loiseau and Nougarede (1963) and by the present writer, is of both morphological and physiological interest from the standpoint of the factors determining 1 Received for publication August 12th, 1963. The author is greatly indebted to Professor C. W. Wardlaw for his helpful discussions of this work, and to Mr. G. Grange for taking the photographs. morphogenetic pattern. This interest is increased and extended by the further observation that, in several members of the Hydrocharitaceae, other cognate, but sometimes less regular, patterns occur. There are also interesting parallels with members of another family of aquatic plants, the Nymphaeaceae. The importance of studying by both analytical and experimental means the factors which control regular and less regular sequences of leaf and bud formation needs no emphasis. The present paper gives a short account of the origin and development of leaves and buds in Hydrocharis and will serve as a basis for accounts of experiments which are in preparation. MATERIALS AND METHODS-The material mainly consisted of turions collected from plants in a local canal and pond, and also of apices of growing stolons. Material was fixed in Craf III (Sass, 1940), dehydrated and embedded in paraffin wax using standard techniques, and stained with safranin, orange G, tannic acid and iron alum (Sharman, 1943). Material to be sectioned longitudinally was first partially dissected and observed under a stereoscopic microscope. Rectangular slices of the turion were then excised in such a way that the sections would pass along a known plane, and fixed and embedded. To facilitate comparison, all illustrations of longitudinal sections are presented with the incipient leaf primordium (and bud, where present) on the right of the shoot apex. Young leaf primordia are called P1, P2, P3 etc., P1 being the youngest visible primordium (Snow and Snow, 1931). MORPHOLOGY OF THE TURION-Two distichous, enveloping scale leaves are present on the outside of the turion. Within these the future foliage leaves occur, in spiral sequence, forming a com-

Abstract: It has been reported that auxin accelerates cytoplasmic streaming at low concentrations and inhibits it at high concentrations in several plant cells. In the present study, the mechanism of inhibition of cytoplasmic streaming by naphthalene acetic acid (NAA) at high concentrations was analyzed in root hair cells of Hydrocharis. Because the effective concentration of NAA inhibiting cytoplasmic streaming decreased when the extracellular pH (pHo) was lowered, it was hypothesized that cytoplasmic streaming is inhibited by NAA via acidification of the cytoplasm. This possibility was supported by the fact that acetic acid, propionic acid and decanoic acid also inhibited cytoplasmic streaming at low pHo. Acidification of the cytoplasm disturbed the orientation of actin filaments (AFs) and disrupted cortical microtubules (MTs). The effects of NAA were reversible; both cytoplasmic streaming and organization of the cytoskeleton were recovered upon removal of NAA. During the recovery, tracks of cytoplasmic streaming in the subcortical region temporarily showed a helical pattern along the longitudinal direction of the cell. Fluorescence staining of cytoskeletons revealed that both AFs and MTs aligned obliquely to the longitudinal axis of the cell. The helical streaming returned to the original reverse fountain streaming after several hours. The simultaneous changes in the organization of both cytoskeletons supported our previous report that the organization of AFs is regulated by MTs.