88 



The Ohio Naturalist. 



[Vol. IV, No. 4, 



expansions homologous to the expansions found in Zostera and 

 other genera of the Helobiae. 



It appears to the writer that the supposition that all so-called 

 cotyledons are homologous is probably erroneous. The type of 

 embryo found in Sagittaria and Alisma is in fact rather excep- 

 tional among Monocotyls and must be regarded as ideal rather 

 than typical of the class. Neither is the fact that the plumule 

 develops as a terminal structure to be regarded as at all conclusive 

 for it is said that the plumules in Dioscoreaceae and Commelina- 

 ceae are apical. There are also a number of fundamentally differ- 

 ent types of Dicotyl embryos. Instead of having two general 

 types in Angiosperms there are several types, and these approach 

 each other at various points in widely separated orders. The 

 division line between Monocotyls and Dicotyls is, after all, not 



.P/v:^-l .W.^e^-*n Af^no.^i, ,,^^;,^^^^ ;^^^^ 



Fi^. 2. Diagram of relationship between Helobiae, Nymphaeaceae and 

 Ranales. 



very distinct. Although Angiosperms are far removed from all 

 other plants, they represent such a vigorous modern group that 

 there has not been time for the extinction of intermediate forms. 

 With the removal of a few connecting groups it would be more 

 easy to recognize six or seven classes of Angiosperms instead 

 of two. 



With our increasing knowledge of the embryogeny of Angios- 

 perms it is becoming more and more apparent that the mere 

 difference in the character of the embryo is not sufficient to deter- 

 mine the position of a genus or family. All pos.sible characters 



