摘要:

SUMMARYThe morphology of the family is described with particular reference to the size and form of the leaf. The salient anatomical features, presented in detail for the individual genera on pp. 19–41, are discussed in relation to the aquatic environment of the plants and to the taxonomy of the family. Characters of taxonomic significance are too few to be of more than limited diagnostic value within the family, but their full significance becomes apparent when the taxonomic position of the Alismataceae is considered in relation to that of other families of Monocotyledons as well as to the Ranunculaceae amongst the Dicotyledons. The anatomical evidence does not appear to support the commonly held view that the Alismataceae and Ranunculaceae are closely related to one another. In spite of the limited value of taxonomic characters within the family it has been possible to present a numerical evaluation of the affinities between the species. Some measurements of the xylem elements are given and their taxonomic and phylogenetic significance is discusse

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYThe Tuberosum Group of potatoes is thought to have originated by selection from a number of representatives of the Andigena Group introduced into Europe nearly 400 years ago. In an effort to define the evolutionary changes that occurred, experiments to compare the growth characteristics of the two groups were carried out. The leading difference between the two groups lies in response to day‐length and adaptation to the long‐days of Europe brought with it a nexus of associated morphological characters. It is shown that the main difference in morphology of the leaves lies in linear dimensions of the parts distal to the petiole and that either single measurements or three measurements combined as a discriminant function provide an evolutionary metric which, when applied to potatoes of various known age, serves as an index of change. The results indicate that the European potatoes changed little from Andigena until the nineteenth century when rapid and sustained evolution took place. The main feature of the evolution of the Tuberosum Group was response to natural selection for long‐day tolerance and blight resistance imposed automatically by the conditions of cultivation and this is being tested experimen

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYApodachlyella complete(Humphrey) Indoh has been rediscovered after more than 20 years and its position as a monotypic genus of the Leptomitaceae is confirmed by its segmented hyphae containing cellulin granules and the lack of a basal cell to the mycelium.The peculiar antheridial development previously described has not been found; the antheridia are essentially the same as those of the Rhipidiaceae, which are also borne on narrow, unsegmented branches arising from segmented hyphae.It possesses certain features which resemble the homologous structures of some Sapro‐legniaceae, notably the distribution of cytoplasmic parts in the mature oospore and the variable number of oospores in the oogonia. It differs from all other Saprolegniaceae and Leptomitaceae in the lack of a basal septum to the oogonium.Nonsexual reproduction has not yet been established forA. completaand merits further investigatio

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYMorphology of the spores, prothalli and juvenile leaves of 6 spp.of Pellaea.and 2 spp. ofNotholaenais described. The spores are trilete and possess a crassimarginate laesura. The exine is psilate and there is a distinct psilate perine inNotholaena.In most species ofPellaeathe exine is psilate, but there is a perinous ornamented outer layer closely adhering to it: the exine is spinulose and a perinous layer is absent inP. falcataandP. rotundifolia.The germ filament is composed of short, thick cells. A prothallial plate is formed by longitudinal divisions of the anterior cells when the germ filaments are 4–10 cells long. In some species, the terminal cells of the filament are sluggish and are often pushed aside by expansion of cells behind them. Young prothalli are usually ameristic but a sluggish obconical apical cell may be differentiated in some species. As the prothallus grows, the apex becomes notched and cordate. Cells behind the apical notch then constitute an apical meristem. Formation of a midrib is initiated when the prothalli are 5–6 weeks old.P. doniana, P. falcataandP. rotundifoliaare sexually reproducing species and develop cordate naked prothalli with thin midribs bearing sex organs. The others are apogamous and the prothalli, soon after the development of a cordate apex, become irregular in shape. Apogamous development of the sporophyte is initiated by the formation of a multicellular cushion on the lower surface of the thallus, generally behind the apical notch: on highly lobed thalli the major lobes may develop a separate sporophyte on each. The cushion develops glandular hairs and paleae similar to those on the sporophyte and grows out as a flat, hood‐like protuberance in which a 3 ‐sided meristematic cell may soon be developed. The hood grows out as the 1st juvenile leaf and often a second leaf is soon developed near its base. A stem apex is differentiated by cells close to the leaf base and further leaves are formed. No roots are produced till the sporophyte develops 3 or 4 leaves. Vascular elements are developed in the apogamous cushion early in development and often extend into the prothallial tissue below. The lamina of the early juvenile leaves is nearly spatulate and entire or faintly lobed: it is naked in the first few leaves, but later, glandular hairs spread from the stipe upwards over the

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00046.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYThe study of pollen development principally inDrosera spathulataandD. capensishas shown that each grain possesses a series of radiating channels passing from its centre to its outer lateral surfaces. Growth or expansion of its cytoplasmic contents causes arms of cytoplasm to protrude through the apertures of these channels. These arms possess a harmomegathic function, i.e. they accommodate expansion or contraction of the tetrads by taking up or losing water. A pollen tube is produced by one such arm in each grain.The attention of biochemists is directed to the fact that callose occurs in massive quantities around the p.m.c. not only inDroserabut probably in most other plant species and would prove a useful source of this material for analysis.

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00048.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1964.tb00043a.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY