28 



It appears more probable that the early Conjugates were filamen- 

 tous forms and that they originated from some other order of 

 green Algae, corning to an abrupt conclusion soon afterwards. 

 Nothing higher was evolved from them, but the group of the 

 Desmidiacese became sharply marked off from the rest of the 

 Conjugates owing to great specialization. The specializing ten- 

 dency was in the direction of a remarkable increase in the com- 

 plexity of morphological characters, and this was accompanied by 

 degeneration of sexual differences. 



Perhaps there may be an affinity between certain of the Con- 

 jugates and the genus Microspora, as the resemblance between 

 such species as Microspora Lofgrenii Nordst. 1 and Zygnema 

 pachydermum West 2 is most striking; the cell- walls are thick 

 and exhibit the same structure, and in both plants precisely 

 similar aplanospores are formed in identically the same manner. 



It is now necessary to consider a group of Alga3 for which 

 Borzi 3 proposed the name of the ' Confervales.' In this order he 

 included a number of Algse which had previously been scattered 

 amongst various groups of the Chlorophycese. The characters of 

 the group are based upon the structure of the cell, which contains 

 parietal discoidal chromatophores of a yellowish-green colour and 

 without pyrenoids. Even the zoogonidia possess discoidal chroma- 

 tophores of a yellowish-green colour and two unequal cilia (some- 

 times one ?). The plants may be unicellular, coenocytic or multi- 

 cellular, and include amongst others the following genera : 

 Ophiocytium, Characiopsis, Chlorothecium, Mischococcus, Tribonema 

 (Conferva), Botrydiopsis and Botrydium. Bohlin 4 in 1897 con- 

 clusively demonstrated, by an exhaustive study of the structure of 

 the cell-wall, the close affinity which exists between the genera 

 Ophiocytium and Tribonema (Conferva); and, in addition, in the 

 earlier stages of development these two genera, one of which is 

 unicellular and the other multicellular, much resemble each other 5 . 

 The order Confervales is subdivided into three families: (1) Tri- 

 bonemacese, which includes Tribonema (Conferva}, Ophiocytium, 



1 Nordstedt in Botaniska Notiser, 1882, p. 55 ; W. & G. S. West in Journ. Bot. 

 Febr. 1897, p. 34. 



- West in Journ. Linn. Soc. Bot. xxx, 1894, p. 266, t. xiii, f. 1 16. 



3 Borzi in Boll, della Soc. ital. dei Microscop. i, 1889. 



4 Bohlin in Bihang till K. Sv. Vet.-Akad. Haudl. 1897, Bd xxiii, no. 3. 



5 Bohlin I.e. t. ii, f. 47, 51, 52, 5456: Wille in Ofvers. af K- Vet.-Akad. Forh. 

 1881, no. 8, t. ix, f. 15, 17, 18, 2126; G. S. West in Journ. Bot. Mar. 1899, p. 106, 

 t. 394, f. 1822. 



