5S8 PAPENFUSS 



ception of the genera comprising the Fucales (and a number of genera which 

 apparently have lost sexuality), the majority of forms show an alternation of 

 generations. In some the two generations are morphologically similar, in others 

 they are dissimilar. 



The knowledge on the developmental and nuclear cycles and the anatomy 

 of brown algae that has accumulated during the past fifty years has naturally 

 had far-reaching e'ffects on the classification of these algae. Ten of the eleven 

 orders of brown algae currently accepted were erected between 1917 and 1926. 



RHODOPHYCOPHYTA 



By the turn of the century a good deal of information had accumulated 

 about the anatomy and sexual reproduction of the red algae. It had been 

 shown that in many of them the fertilized carpogonium establishes a connection 

 with a neighboring cell, named the auxiliary cell by Schmitz in 1883, that the 

 fertilized egg nucleus migrates into the auxiliary cell, and that the cystocarp 

 develops from this cell. 



The nuclear cycle, especially the place of meiosis in the life history, had as 

 yet not been studied. Yamanouchi, about fifty years ago (1906a, b), first 

 worked out the nuclear history and showed that in Polysiphonia the plants 

 which bear tetrasporangia are diploid and that meiosis occurs in the tetra- 

 sporangium. The confirmatory cultural evidence was supplied by Lewis in 

 1912. Thus at last was determined the long-misunderstood role of the tetra- 

 sporangia in the life history of the red algae. As late as 1904 Oltmanns, in 

 agreement with several earlier authors, had still regarded the tetrasporangia 

 as accessory reproductive organs of the gametophytic generation. 



Svedelius (1915), studying the development and cytology of Scinaia, a 

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

 occurs soon after fertilization of the egg nucleus. Such species (the majority 

 of Nemalionales) consequently lack free-living tetrasporophytes. It is now 

 well established that the majority of red algae above the Nemalionales possess 

 three generations: a haploid gametophyte (which is usually dioecious), a 

 diploid carposporophyte which is permanently attached to and largely parasitic 

 on the gametophyte, and a diploid free-living tetrasporophyte, whereas in the 

 majority of Nemalionales the life history includes only two generations, a 

 haploid gametophyte and a haploid carposporophyte. 



We now also know that in a number of genera of red algae the life history 

 deviates from the two general types outlined above. Of special interest is the 

 condition that obtains in two genera of the Nemalionales. In four species of 

 Liagora (B0rgesen, 1927; Kylin, 1930; Yamada, 1938; Levring, 1941; Ab- 

 bott, 1945) and in one of Helminthocladia (Feldmann, 1939) the carposporo- 

 phyte forms tetrasporangia in the place of carposporangia. The cytology of 

 these species has not yet been studied, but it is believed that in them meiosis. 



