Algae and the Principles of their Evolution . 99 
those of the Desmidiaceae. Rooting hairs are not only known 
in the true Chlorophyceae but also in the Conjugatae 1 , and the 
equality of the cells of the filaments is a very common character 
in both groups. 
With respect to the Siphoneae, which constitute a very 
special group, I think that the Vaucheriaceae can be detached 
from them with even more reason than the Conjugatae from 
the true Chlorophyceae. The multiplicity of the nuclei is not 
only common to the Siphoneae but also to many Chloro- 
phyceae at an adult stage of their cells (Cladophoraceae, some 
Pediastreae) 2 . 
In this paper I shall set aside those orders which by the 
fixity of their characters, or their morphological differentiation, 
constitute very peculiar and definite groups among the 
Chlorophyceae. 
Chlorophyceae 
A. Euchlorophyceae 
Flagellatae— ^ V olvocincac t)oln^nlln/.nnQ 
Conjugatae 
Chaetophoraceae 
Sphaeropleaceae, Oedogoniaceae C oleochaetaceae 
As in similar cases, the proper course to adopt in order to 
discover affinities is to ascertain the complete development of 
each type under consideration, and to find out the modifications 
it undergoes under various circumstances, both in its natural 
habitat and also under cultivation. 
1894; and Chodat, Histoire des Protococcoidees, Bull. Herb. Boissier, IV, 1896, 
p. 277. 
1 Borge, Ueber die Rhizoidenbildurig, Upsala, 1894. 
2 Askenasy, Ueber die Entwicklung von Pediastrum , Ber. d. D. Bot. Gesellsch., 
1888, Heft 3. And also Chodat et Huber, Recherches experimentales sur 
Raphidium , Bull. Soc. Botan. Suisse, 1895, t. v. 
