NUCLEAR and SOMATIC PHASES IN THE FLORIDEAE

Summary (i) The need for a considerable extension of morphological and cytological work in the Florideae is pointed out. (2) Before proceeding to the survey current terminology is reviewed; some terms are discarded and definitions are given for those retained. The survey shows that our cytological knowledge is limited almost entirely to two of the six orders, the Nemalionales and Ceramiales. Members of the Nemalionales show great variety as regards the somatic phase sequence in the life history. Species investigated cytologically, to varying degrees of detail, are all of the Nemalion type, that is, two morphologically dissimilar haploid phases separated by a very short diplophase of the nucleus. The Gelidiales have been completely neglected, and apart from Corallina officinalis var. mediterranea so have the Cryptonemiales. In this latter order there are indications of ‘atypical’ phase sequence. This is also true of the Gigartinales which include in addition forms showing the Phyllophora Brodiaei type of life history, i.e. two morphologically dissimilar phases, one a gametophyte and the other a tetrasporic nemathecium developed from the auxiliary cell. The nuclear phase sequence is unknown. Information about the nuclear history in the Rhodymeniales is only sufficient to indicate problems in need of investigation. In the Ceramiales the Polysiphonia type of life history with three somatic phases (two morphologically similar) and two nuclear phases appears to be general, and detailed accounts of such exist for several species. Other types are known and representatives have been investigated: Spermothamnion Turneri has been shown to be cytologically polyphasic and to be characterized by the formation of functional sexual organs on the diploid; the polysporangium of S. Snyderae has been shown to be a compound tetrasporangium, and Plumaria elegans has been found to have three nuclear phases, the triploid bearing a special type of sporangium. In addition, some species show unusual somatic phases sequences, the nuclear phases being unknown. (3) Three lines of cytological research are envisaged associated with ecological and physiological investigations. (4) There is a striking absence of physiological concepts concerning the Florideae and hence the need for pure culture and general physiological investigations. I wish to express my thanks to Prof. C. W. Wardlaw for his stimulating interest and help in the preparation of this article, and also to the Council of the University of Manchester for library facilities. Thanks are also due to Mr E. Ashby for his help in the production of the figures. Owing to war‐time restrictions direct copying of previously published figures has not been possible. Instead they have been photographed and magnified considerably in order that the photographic image could be meticulously picked out in Indian ink. Subsequently the diagram was cleared by bleaching and reduced to its original size. I trust that faithful copies of the originals, as published, have thus been obtained.