ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1945.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Summary(1) Some of the developments which have made for a fuller understanding of the shoot apex in pteridophytes are discussed, particular attention being paid to morphogenetic processes, (2) Of the several interpretations of growth and cellular arrangement at the apex which have been advanced, that of Naegeli, in which the importance of the apical cell is emphasized, appears to be most applicable to the livingpteridophytes; Sachs's geometrical‐mechanical views emphasize another aspect of organization at the shoot apex, while his comprehensive outlook on the nature of the meristematic region as a whole deserves careful attention. (3) In the pteridophytes, with some exceptions, there is no obligate relation between apical segmentation and organogenesis and histogenesis, i.e., segmentation does not determine organogeny. (4) The value of the facts of apical segmentation in phylogenetic studies is discussed. (5) The history of causal morphology is briefly outlined. If the phyletic history of plants were before us in full, the problems of causal morphology would still remain. These includethe external and internal factors which determine morphogenetic processes and specific structural organization. (6) The development of leaf primordia in ferns and in dicotyledons is compared: the data show that a knowledge of the fern leaf may be regarded as essential to any general theory of leaf development. Such a theory must include a consideration of spatial, metabolic and mechanical factors. (7) The view is developed that shoot buds in ferns occupy an interfoliar position at the time of their inception, the position which they eventually occupy on the shoot or leaf base being determined by the distribution of growth. Bud development thus requires a study of the integrated growth activities at the apex. (8) An account is given of the initial and subsequent differentiation and development of vascular tissue at the shoot apex; spatial, metabolic and mechanical factors which may be implicated are discussed. The view‐is held that the structural arrangements observed should be interpreted in terms of growth and not of adult functional activities. (9) Views based on comparative studies which relate to the fundamental nature of the shoot are of two kinds, i.e. axial and phytonic, a constructional unit being taken for granted‐in each case. It is anticipated that investigations of the growing point from the standpoint'of causality may eventually lead to new concepts regarding the shoot type of organization. An indication is given of some of the factors which may lend themselves to further investig

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1945.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

SummaryThe last 15 years have seen notable advances in knowledge of the distribution of chlorophylls, carotenoids and other pigments in the algae, in the structures and function of individual pigments, and in their correlation with morphological characteristics. The algal classes are often associated with specific colouring matters or fairly well‐defined mixtures thereof, so that detailed knowledge of the pigmentation is not without phylogenetic value.The Chlorophyceae contain chlorophyllaandb, zeaxanthin and lutein, together with a minor proportion of less typical carotenoids. In general the quantities and proportions do not diverge greatly from those found in higher plants; green algae cultured under abnormal or artificial conditions often develop unusual pigmentation though experience is here rather limited. In view of what has become known of the role played by carotenoids in the sexual reproduction ofChlamydomonas eugametos, particular interest is attached to the differential pigmentation of gametes, antheridia and oogonia of many of the Chlorophyceae. Quantitative and qualitative examination of Xanthophyceae, Chrysophyceae, Dinophyceae, Cryptophyceae, Chloromonadineae and Euglenineae is less complete, but it is certain that chlorophylla, carotenes, and xanthophylls are still the main pigments though other carotenoids which have hitherto appeared to be characteristic of other algal classes (e.g. fucoxanthin) or higher plants (e.g. flavoxanthin and taraxanthin) are occasionally encountered. Some of the algae of these classes contain characteristic carotenoids (diato‐ and diadinoxanthin in diatoms, peridinin and dinoxanthin in dinoflagellates) though their general distribution has yet to be examined; the detailed chemical nature of these materials remains obscure, and its elucidation is complicated by the pigments assuming labile forms which may be present in the algae or formed by chemical treatment. The diatoms are distinguished also by chlorophyllcwhich has been found as well in some of the Phaeophyceae. The brown algae have long been thought to contain no more than traces of chlorophyllb, a view substantiated by modem analyses, so that the new chlorophyll may replace chlorophyllbof other algae and higher plants, and is perhaps to be correlated with photosynthetic activity as indicated by typical reserve materials. The Phaeophyceae, in addition to carotenoids common to most algae, are characterized by fucoxanthin and nearly related pigments which assume a degree of photo‐synthetic activity: quantitatively, however, the brown algae are not richer in carotenoids when compared with other algae, for an excess of fucoxanthin is balanced by a deficiency in other polyene pigments. The Rhodophyceae contain no chlorophyllb, but here the deficiency is to some extent made good by a recently discovered pigment, chlorophylld.The total chlorophyll content is nevertheless low compared with that of the green algae, part of the photosynthetic activity being due to phycobilins which occur also in the Cyanophyceae. The blue‐green algae are in turn outstanding in exhibiting a series of new carotenoids, perhaps of photosynthetic value; of these myxoxanthin and myxoxanthophyll seem to be as characteristic of the Cyanophyceae as, for example, fucoxanthin is of the Phaeophyceae.The chemistry of the algal pigments which are common in higher plants has been adequately reviewed elsewhere, but a section of the present account is devoted to the salient features of purely algal colouring matters, especially chlorophyllcandd, the phycobilins, and characteristic algal carotenoids mentioned above.An outstanding result of algal pigment research has been the demonstration that here phycobilins and carotenoids are not, as has been assumed of similar pigments of higher plants, merely precursors or degradation products of chlorophyll, but possess a degree of photosynthetic activity enabling the organism to take advantage of conditions of habitat where chlorophyll is less efficient. Much more remarkable, however, is the demonstration of the effect of certain carotenoids on the reproductive processes inChlamydomonas, a brief review showing that such diverse phenomena as formation of flagella in gametes, motility, fertilization and relative sexuality are brought about by a group of pigments of which our knowledge is, in view of their complex nature, unusually complete.My thanks are due to Prof. I. M. Heilbron, D.S.O., F.R.S., for his interest and encouragement during the preparation of this

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1945.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY