184 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



"VVille in 1894, working on Nemalion, saw the actual fusion of the male and 

 female nuclei, an observation that was confirmed a few years later by Osterhout 

 (1900). Yamanouehi (1906a, 1906b) first worked out the nuclear cycle and 

 showed that the red algal genus Polysiphonia possesses an alternation of genera- 

 tions between haploid gametophytic and diploid tetrasporangial plants, with 

 meiosis occurring in the young tetrasporangium. Thus at last was determined 

 the long-misunderstood role of the tetrasporangia in the life history of these 

 plants. 



The correctness of Yamanouchi's observations was confirmed by Lewis (1912) 

 by cultural studies. Svedelius (1915), studying the development and cytology of 

 Scinaia, a genus which was known to lack tetrasporangia, established that in it 

 meiosis occurs immediatel}^ after fertilization. Such species (the majority of Ne- 

 malionales) consequently lack free-living tetrasporophytes. The observations 

 of Svedelius were quickly confirmed by Kylin (1916) and Cleland (1919). A 

 number of Florideophycidae — members of both the Nemalionales and of some 

 of the orders above them — -were later found to have life cycles that deviate from 

 the two general types referred to above. For a review of these the reader is re- 

 ferred to the papers by Drew (1944) and Papenfuss (1950b). 



Oltmanns (1898, p. 138; 1904, p. 537) in agreement with Harvey (1849) 

 and certain other early writers regarded the tetrasporangia as accessory repro- 

 ductive organs. He considered the plant that produces the sex -organs as the 

 gametophyte and the gonimoblast as the sporophyte (the carposporophyte of 

 Church, 1919b, p. 331). From the cytological work of Yamanouehi, Lewis 

 (1909), and many later investigators, it is now well established that the ma- 

 jority of red algae above the Nemalionales possess three generations: a haploid 

 gametophyte, a diploid carposporophyte which is permanently attached to and 

 largely parasitic on the gametophyte, and a diploid, free-living tetrasporophyte. 

 For an interesting account of the history of the discovery of an alternation of 

 generations in the red algae the reader is referred to a paper by Svedelius 

 (1916). 



Feldmann (1952) is of the opinion that all Florideophycidae that lack a free- 

 living tetrasporophyte are derived. Although this is unquestionablj^ true of a 

 number of forms — for example, certain species of Phyllopliora, Gymnogongrus, 

 and Ahnfeldtia — it may be questioned whether this is also true of those Nema- 

 lionales in which meiosis occurs immediately after fertilization (the majority 

 of species in the order) or at carpospore formation. Svedelius (1953, p. 80, fn.) 

 has promised to deal with this question. 



Although credit must go to Lamouroux (1813) for first recognizing the red 

 algae as an autonomous group of plants, he, like his predecessors (e.g., Gmelin, 

 1768), and contemporaries (e.g., Esper, 1797-1808, and Turner, 1802, 1808, 

 1809, 1811, 1819), did not depart from Linnaeus (1753) in classifying these 

 algae almost entirely on their external features, even if in much greater de- 

 tail than Linnaeus. This very frequently resulted in the placing together of 

 totally unrelated forms or in the separation of related forms. 



C. Agardh (1824, 1828) was the first to take into serious consideration in 

 the classification of the algae the structure of the thallus and of the reproduc- 

 tive organs, even if only as regards their gross structure. With C. Agardh thus 

 begins what Sjostedt (1926, p. 78) has termed the anatomical period in the 



