140 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



In 1925 (a) Pascher gave a treatment of the class in his Siisswasserflora 

 Beutschlands. . . At this time he established the order Rhizochloridales to receive 

 the amoeboid forms. More recently Pascher (1937-1939) has produced, as a 

 volume in the second edition of Rabenhorst's Kryptogamen-Flora von Deutsch- 

 land . . . , a monumental work of 1092 pages on the morphology and taxonomy of 

 the known Xanthophyceae of the world. In this work Pascher recognized some 

 89 genera of which he alone authored 60. 



In 1930 Allorge proposed the designation Xanthophyceae as a substitute for 

 Heterokontae, and since this appellation conforms to the majority of class names 

 of algae in connoting color and in terminating in -phyceae, it has met with fa- 

 vor in many quarters. 



Significant evidence supporting Pascher's (1914, 1921) conclusions of a re- 

 lationship between Xanthophyceae and Chrysophyceae was furnished in 1931 

 and 1938 by Vlk who established that the biflagellate motile cells of Xantho- 

 phyceae agreed with those of Chrysophyceae in that the long flagellum is of 

 the tinsel type, being beset with two rows of delicate cilia, whereas the short 

 flagellum lacks cilia. 



Further facts favoring this alliance were brought to the foreground by Pascher 

 in 1932. He pointed out that the bivalved endogenously produced cysts which 

 he had discovered in certain Xanthophyceae in 1930 (1930a, p. 406, fig. 3c; 1930c, 

 pp. 332-335, fig. 17; see also Pascher, 1937, pp. 71-78, figs. 56-63) were similar 

 to the bivalved cysts characteristic of the Chrysophyceae. 



Of especial interest is the abundant evidence brought forth in recent years 

 indicating that the classical Yaucheria actually belongs in the Xanthophyceae 

 rather than in the Chlorophyceae (Seybold, Egle, and Hiilsbruch, 1941; Chade- 

 faud, 1945; Strain, 1948; Koch, 1951). It will be recalled that Bohlin (1901) and 

 Blackman and Tansley (1902) had placed Vaucheria in the Xanthophyceae. In 

 general, however, phycologists have preferred to retain the genus in the order 

 Siphonales of the green algae. Egerod (1952, p. 336) has assembled the facts 

 in support of the inclusion of the Vaucheriales in the Xanthophyceae, the most 

 important of which are: (1) the unequal length of the flagella of the sperm 

 (Pringsheim, 1855, p. 142; AValz, 1866-1867, p. 134, pi. 12, fig. 4; Woronin, 

 1869, p. 156; Strasburger, 1887, p. 396; Koch, 1951); (2) the ciliated condition 

 of the shorter flagellum of the sperm (Koch, 1951) ; and (3) a pigment complex 

 comparable to that of Xanthophyceae (Seybold, Egle, and Hiilsbruch, 1941; 

 Strain, 1948). It is to be noted, however, that Vaucheria is reported as possessing 

 only chlorophyll a whereas Trihonema, the only other member of the class whose 

 green pigment has been analyzed (Strain, Manning and Hardin, in Strain, 1951, 

 p. 247 and table 1), possesses chlorophyll a and e. 



In 1948 Mangenot produced evidence for the removal of PhyUosipJwn from 

 the Chlorophyceae to the Xanthophyceae, where Blackman and Tansley (1902) 

 had once accorded it a position. 



The following classification of the Xanthophyceae is largely based on that 

 of Pascher (1937-1939). 



Class Xanthophyceae Allorge (1930, p. 230) 

 Syn.: Heterokontae Luther (1899, p. 17) 



Order HETEROCHLORIDALES Pascher (1912b, p. 10) 



Syn.: Series Chloramoebales Fritsch, in West (1927, pp. 300, 301); Xantho- 

 monadales Chadefaud (1950a, p. 790) 



