THE ROLE OF STUDY OF ALGAE IN DEVELOPMENT OF BOTANY 473 



unicellular, free-floating, and sessile forms whose life cycle involves a forma- 

 tion of motile cells of a gymnodinoid nature. These botanists held that the 

 immobile phase is comparable to that of unicellular coccoid Chlorophyceae 

 and that the motile phase is zoosporic in nature. Many protozoologists held 

 that the swarmers are dinoflagellates and that the coccoid phase in the life 

 cycle is cyst-like in nature and comparable to the cysts known to be formed 

 by many dinoflagellates. In 1927 Pascher gave further evidence supporting the 

 view of botanists. This was the discovery of multicellular branched and un- 

 branched filamentous algae whose zoospores have a structure typical of 

 dinoflagellates. The argument for including the chrysomonad flagellates among 

 the algae rests on a greater number of cases. There are a considerable number 

 of multicellular algae with swarmers typical of chrysomonads, a fact which 

 seems to warrant inclusion of chrysomonad flagellates among the algae. 



Taxonomists have long been interested in a natural classification of the 

 plant kingdom but differ with regard to the primary taxa that should be rec- 

 ognized. Today there are two schools of thought concerning the number of 

 divisions into which the plant kingdom should be segregated. One school 

 follows the idea that the most primitive of the plant kingdom is the Thallo- 

 phyta, which consists of two subdivisions, the Algae and the Fungi. Accord- 

 ing to this system the various distinctive series of algae are each given the 

 rank of a class in the subdivision Algae. The second school holds that differ- 

 ences among the algae are of sufficient magnitude to preclude grouping of 

 them in a single subdivision or even division. According to this conception 

 the algae should be segregated into more than one division. All systems adopt- 

 ing this idea follow in general the proposals of Pascher (1914, 1921, 1931a). 

 He holds that certain classes of algae, as the Rhodophyceae and the Phaeo- 

 phyceae, differ so markedly from other algae that they merit the rank of 

 divisions. Other classes of algae, as the Chrysophyceae, Xanthophyceae, and 

 the Bacillariophyceae (diatoms) are thought to have sufficient in common 

 to warrant inclusion in a single division. European botanists, especially the 

 British, generally adhere to systems which place algae in a subdivision of the 

 division Thallophyta. Many American botanists prefer those systems which 

 abandon the division Thallophyta and which segregate algae into a number 

 of divisions. 



The foregoing discussion of progress in taxonomic study of algae may have 

 left the impression that the primary concern of phycologists has been that 

 of floristic studies and arrangement of algae according to a natural system. 

 This is far from the case. The structure of reproductive organs, especially 

 those of Chlorophyceae and Phaeophyceae, is so simple and so easily observed 

 that it attracted the attention of phycologists almost as soon as the compound 

 microscope supplanted the hand lens in the study of algae. Vaucher (1803) 

 was one of the first in this field. He studied reproduction in a number of algae 

 and in "Ectosperma" (now known as Vaucheria), and he described and fig- 



