igos.] OF THE ANCESTORS OF THE PLANT KINGDOM. 95 



It is the tetrasporine tendency which has been the permanent one 

 and has resulted in producing the higher green plants. This condi- 

 tion in Chlamydommias resulted in the production of a series of 

 plants which gradually replaced the formation of zoospores by that 

 of vegetative cell division. The resulting family was the Palmel- 

 laceae, the one which formed the starting point in the development 

 of the algae, according to Chodat. While there seems to be but little 

 question that the Palmellaceas have given rise to most of the other 

 families of the green algae, there is every evidence that it was itself 

 derived from. Chlamydonionas , rather than the reverse, as contended 

 by Chodat. 



It is impossible at this time to even indicate the development of 

 the higher algae from the Palmellaceae. With the exception of the 

 Confervales, which seems to have developed independently of the 

 typical green algae, and the Conjugales, which apparently have arisen 

 directly from the Chlamydonionas type, all the higher green algae 

 can be traced back through the Palmellaceae with considerable cer- 

 tainty to their Chahnydonionas ancestor. The Conjugales have 

 always been a stumbling block in constructing any developmental 

 line of the algae from primitive forms. But granting that the fila- 

 mentous Conjugales, as well as the desmids, are unicellular (the 

 reasons for which can not now be given) it is comparatively easy 

 to find the origin of the conjugation habit so emphasized in this 

 group, in Chlamydonionas Braunii. In this species the female or 

 receptive cell comes absolutely to rest before fertilization and the 

 smaller or male cell becomes attached to it. Then the entire con- 

 tents of the male cell passes into the female cell, leaving behind the 

 empty cell wall, just as in some of the desmids and in most of the 

 filamentous-like Conjugales. 



The more the genus is studied the more reasonable becomes the 

 conclusion that Chlamydonionas has not only given rise to such an 

 aberrent group as the Conjugales, but that it may safely be regarded 

 as the phylogenetic starting point of the various lines of ascent in 

 the true green algae. At present in the higher algae the Chlamy- 

 donionas stage is, of course, retained in the zoospore and the gamete, 

 a vegetative non-motile generation being interpolated between either 



PROG. AMER. PHIL. SOC. XLVU. 1 88 G, PRINTED JULY II, I908. 



