PAPENFUSS: CLASSIFICATION OF THE ALGAE 171 



class, the Heterogeneratae, comprised forms which showed an alternation of 

 heteromorphic generations. It included two subclasses, the Ilaplostichineae 

 and the Polystichineae. In the Ilaplostichineae no intercalary longitudinal di- 

 visions occur in the thallus and consequently no true parenchymatous tissues 

 are formed. In the Polystichineae intercalary longitudinal divisions are formed 

 and hence true parenchymatous tissues are produced. The Ilaplostichineae re- 

 ceived the orders Chordariales, Sporochnales, and Desmarestiales, whereas the 

 Polystichineae received the Punctariales, Dictyosiphonales, and Laminariales. 

 The third class, the Cyclosporeae, received the single order Fucales. 



The separation of the Ectocarpales sens^l Oltmanns (1922b) into haplosti- 

 chous and polystichous groups was first proposed by Kuckuck {in Oltmanns, 

 1922b; 1929). It is to be noted, however, that Kylin employed this character 

 only with reference to the Heterogeneratae. Papenfuss (1947) has merged the 

 Punctariales in the Dictyosiphonales. It would seem that Kylin (1947) also 

 arrived at the conclusion that these two orders are synonymous, since in the 

 body of his paper he placed Bictyosiplwn in the Punctariales even though in 

 the introduction (p. 4) he accepted both orders. Arasaki (1949) argues in favor 

 of retention of both orders but the evidence produced is hardly sufficient. 



The system of Kylin has received wide recognition. Among those who have 

 not accepted it or have accepted it only in part are Hygen, Fritseh, and more re- 

 cently Papenfuss. Hygen (1934) is dissatisfied with Kylin 's arrangement largely 

 because the Isogeneratae includes a heterogeneous assortment of algae that 

 could not be regarded as forming a phylogenetically coherent unit. 



Fritseh (1943, 1944, 1945) does not accept the orders Chordariales, Punc- 

 tariales, and Dictyosiphonales but retains the families comprising them in the 

 Ectocarpales largely because he believes (1944, p. 254) that their heteromorphic 

 life cycle is derived "by divergent development of the two generations, from an 

 isomorphic alternation, comparable to that exhibited by the Ectocarpaceae." It 

 seems very likely, however, that the other groups with a heteromorphic alterna- 

 tion of generations (the oogamous Sporochnales, Desmarestiales, and Lamina- 

 riales) also evolved, even if not directly, from the Ectocarpales. The Ectocar- 

 pales sensu Fritseh includes a very heterogeneous assemblage of algae. 



Papenfuss (1951b) accepts all the orders recognized by Kylin, except the 

 Punctariales, but rejects the classes Isogeneratae, Heterogeneratae, and Cyclo- 

 sporeae and the subclasses Ilaplostichineae and Polystichineae of the Hetero- 

 generatae. Such an arrangement allows for the parallel and independent evolu- 

 tion of groups with an alternation of isomorphic or heteromorphic generations; 

 it recognizes the Ectocarpales as the possible ancestral stock from which had 

 emerged several orders; and it takes cognizance of the fact that the Fucales are 

 parenchjnnatous (polystichous) and that parenchymatous forms also occur in 

 the Isogeneratae (e.g., Dictyotales, Sphacelariales). In agreement with K.ylin 

 (1933, 1937c, 1938, 1940b) and Fritseh (1945, pp. 380-381), Papenfuss regards 

 the Fucales as occupying an isolated position in the Phaeophyceae. 



Recently Feldmann (1949) established an order Scytosiphonales for certain 

 Dictyosiphonales, but the more significant distinguishing features of the new 

 order are based on the acceptance of observations of extremely questionable 

 accuracy. 



On the basis of pigment composition, the Phaeophycophyta appear to be 



