HISTORICAL EEYIEW OF THE FLOBIDEJ: 303 



jpurifera and D. cocciiiea, Gloiosiplionia, Dasya, and Callithamnion, 

 the jDeculiar nuclear phenomena, as also cytojDlasmic fusion, being 

 solely the expressions of an attempt to obtain food-supplies for the 

 parasitic genei-ation. This has placed the question of the nutrition 

 of the carposporophyte on a rational basis, and older views on the 

 sexual significance of cytoplasmic fusions, unavoidably obscure so lon^i- 

 as the essential nuclear phenomena were little known, even in the case 

 of higher plants, have been relegated to their proper place. 



IV. In more recent times the attention paid since 189-i to the 

 cytological details of diploid phases as associated with the familiar 

 alternation of generations in the life-history of land-plants, and as 

 constituting a causal factor for the differentiation of gametophvte 

 and sporophyte, has led to a more thorough investigation of the 

 reproductive organization of the Floridese. In a paper on I^olysi- 

 phonia vlolacea, SiiiaEO Yama^s'ouchi ^ (Chicago, 1906), the 

 cytological relation of the diiferent individuals of the trimorphic 

 sequence involved in the life-cycle was clearly established as a model 

 for similar w^ork on other forms, as the necessity for the use of the 

 microtome and the best methods of modern technique was success- 

 fully vindicated. So long as algologists could make out nine-tenths 

 of the facts by simple section-cutting, or ' squeezing-out ' methods, 

 the use of the microtome was avoided ; and though the imjjortance 

 of nuclear phenomena may have been exaggerated, these latter are an 

 essential part of the story, and cannot be omitted. However much 

 can be done even better without it ; in dealing Avith the general 

 anatomy and most of the reproductive processes, more particularlv as 

 presented in fresh material, the microtome remains as the last appeal 

 in all cytoplasmic research. 



Even more recently the Floridese maintain their value as con- 

 tributing to the solution of much debated problems of reproductive 

 mechanism common to higher organism. The demonstration by 

 Stedelius 2 of the fact that in such forms as Scinaia (as also by 

 Kylin ^ and Cleland for Ne7nalion) the cytological alternation of 

 haploid and diploid nuclear phases need not necessarily run conform- 

 ably with the morphological alternation of gametoph^^te and sporo- 

 phyte individuals, bids fair to remove the curious obsession of botanists 

 (dating to Strasburger '^, 1894) that such cytological mechanism of 

 the nucleus can ever be a satisfactor}-- causal factor in the differentia- 



^ Yamanouchi (Chicago, 1906), Bot. Gazette, p. 425, "The Life-History of 

 Polysiphonia violacea." 



■^ Svedelius (1915), Nova Acta, Upsala, iv. p. 1. 



3 Kylin (1916), Berichte, xxxiv. p. 257 : Cleland (1919), Ann. Bot. p. 323. 



^ Strasbvirger (1894) may be said to have initiated the idea that since the 

 gametophyte of land plants is haploid in its chromosome number, and the sporo- 

 phyte is diploid, therefore any haploid stage must be a gametophyte, and any 

 diploid generation a sporophyte : a curious non aequitur which has been very 

 generally accepted. 



There cannot be more than two cytological phases, haploid or diploid, but 

 there may be more than two morphologically differentiated stages in a life-cycle ; 

 e. g. the Floridese have three, hence commonly manipulated to make two, in order 

 to suit a preconceived academic scheme. 



