PAPENFUSS: CLASSIFICATION OF THE ALGAE 139 



and made the important discovery tliat the zoospores of these genera likewise 

 possessed two unequal flagella instead of one flagcllum as had been believed. 

 This character was thus found to exist in several genera of the Confervales 

 showing various levels of thallus specialization — flagellated, palmelloid, coccoid, 

 and filamentous types. 



In evaluating the phylogenetic implications of the facts contributed by Borzi, 

 Bohlin, and himself, Luther arrived at the far-reaching conclusion that the 

 characters whereby these algae differed from the Chlorophyceae were of such 

 magnitude that it was no longer possible to retain them in this alliance. Con- 

 sequently, he erected for them a separate class which he named Heterokontae. 

 Luther's class, interestingly enough, corresponded very closely to Borzi's Con- 

 fervales, except that he included in it the newly erected order Chloromonadales 

 (as exemplified by Vacuolaria), as well as the genera Chloramoeha and Chloro- 

 saccus. The Chloromonadina, as typified ]:>y Vacuolaria, had previously been 

 established as an autonomous group of flagellates by Klebs (1892). It is now 

 known that the Chloromonadales w^ere misplaced in the Heterokontae. 



The views of Luther as regards the autonomy of the Heterokontae were 

 quickly adopted by a number of students of the algae, including especially 

 Blackman (1900), Bohlin (1901), Blackman and Tansley (1902), Oltmanns 

 (1904), West (1904), and Heering (1906). Heering gave a comprehensive treat- 

 ment of the forms represented in the flora of Schleswig-IIolstein and a full his- 

 torical review of the class. He also pointed to (as Blackman, 1900, p. 671, had 

 previously done) the striking parallelisms in thallus types between the Heter- 

 kontae and the Chlorophyceae. 



Blackman (1900, p. 674) brought attention to the fact that Vaucheria a;p- 

 peared to be the only "green" alga outside the Heterokontae which had chloro- 

 phyll possessing the same characters as in members of the Heterokontae and 

 wondered what the phylogenetic significance of this would prove to be. A year 

 later, Bohlin (1901) removed the Vaucheriaceae to the Heterokontae and estab- 

 lished for the family the order Vaucheriales. The transfer was made on the 

 basis of the same pigment reaction he had obtained in Tribonema, the presence 

 of discoid plastids, the storage of food as oil, and the observation by Walz (1866- 

 1867, p. 134, pi. 12, fig. 4) that the sperms had two unequal flagella. 



Blackman and Tansley (1902) followed Bohlin in the inclusion of Vaucheria 

 in the Heterokontae and, what is important in the light of Mangenot's (1948) 

 recent corroborative conclusion, they also removed the Phyllosiphonaceae from 

 the Chlorophyceae to the Heterokontae, presumably on account of the storage 

 of oil as a food reserve in this family. 



Following the pioneering studies of Borzi, Bohlin, and Luther, numerous 

 workers, but more especially Pascher, have contributed materially to our knowl- 

 edge of the Xanthophyceae. In 1912 (b) Pascher elaborated upon the earlier 

 systems of classification of the group and in accordance with the morphology 

 of the thallus established orders which paralleled certain chlorophycean orders. 

 He erected the order Heterochloridales to receive the flagellated members, the 

 Heterocapsales for the palmelloid types, the Heterococcales for the coccoid genera, 

 the Heterotrichales for the filamentous forms, and the Ileterosiphonales for the 

 siphonous representatives. As mentioned above, Pascher in 1914 and 1921 brought 

 the Xanthophyceae in alliance with the Chrysophyceae and Bacillariophyceae. 



