562 PAPENFUSS 



istic storage products leucosin and oil in both the pigmented and the colorless 

 members; (3) the three types of flagellation — one flagellum, two unequal 

 flagella, or two more or less equal ones; and (4) the formation of endoplas- 

 matic cysts of a unique type. 



As is true of the Xanthophyceae, the bulk of our knowledge of the 

 Chrysophyceae has been acquired during the past 40 years, mostly through 

 the investigations of Pascher. x\t present the class is credited with some 10 

 orders and a large number of families. Work done during the last few decades 

 has also demonstrated with reasonable certainty that two important groups 

 of the phytoplankton of the sea, the coccolithophores and the silicoflagellates, 

 are chrysophytes. As in the Xanthophyceae, the thalli of Chrysophyceae 

 parallel those of certain orders of the green algae. 



Bacillariophyceae. Klebahn in 1896, working on Rhopalodia gibba, a 

 member of the order Pennales, was the first to obtain cytological results sug- 

 gesting that diatoms are diploid and that meiosis occurs during gametogenesis. 

 Since that time various authors (Karsten, 1899, 1912; Geitler, 1927a, 1927b, 

 1928; Cholnoky, 1928, 1933a; Meyer, 1929; Subrahmanyan, 1947) have con- 

 firmed the fact that the Pennales are diploid and that meiosis precedes auxo- 

 spore formation. 



As a conjugation of cells was not known to occur during auxospore forma- 

 tion in the Centrales, it was believed for a number of years (cf. Oltmanns, 

 1922) that these forms, to the contrary, are haploid and that in them auxo- 

 spore formation is an asexual process. Persidsky (1929, 1935) first showed 

 that the Centrales are likewise diploid and that here auxospore formation is 

 also a sexual process (autogamy). His observations have been confirmed by 

 Cholnoky (1933b) and more particularly by Iyengar and Subrahmanyan 

 (1942, 1944), Stosch (1951a), and Geitler (1952). The evidence at hand 

 indicates, therefore, that the Centrales and Pennales are not as remote from 

 each other as has been supposed. 



In 1897 Murray observed in certain marine members of the order Centrales 

 rounded protoplasmic bodies which he interpreted as reproductive cells. Later 

 these so-called microspores were observed by a number of investigators in 

 various marine and fresh-water Centrales. In some instances the microspores 

 appeared to be provided with two lateral and in others with two terminal 

 flagella of equal length. Stosch (1951a, 1954) observed with certainty only 

 one flagellum. It was thought that these microspores may be gametes, but 

 proof of this was not forthcoming until 1951 (a, b) when Stosch showed that 

 in some species they actually are male gametes (see also Stosch, 1954; Geitler, 

 1952). The establishment of the occurrence of flagellated cells in the diatoms 

 is a discovery of far-reaching significance. 



