Evolution of Plants 365 



spore cavities. This is further emphasized by future behavior 

 of the cells. For in Ephedra the outer prothallial cells become 

 structures that push out into the megasporangial tissue and 

 there absorb nourishment; in Casnarina the resulting cell- 

 groups to the number of 10-20 grow downward as mature 

 megaspores or embryo sacs into the megasporangial tissue, and 

 there act in part as absorbers. 



The next stages are of special interest, as probably affording 

 a direct connection in the relation of Ephedra and other gymno- 

 sperms as to formation of their egg-cells, to the condition as 

 it occurs in angiosperms. 



In Ephedra the prothallial tissue, as it forms within the 

 megaspore, shows rough division into an inner or antipodal 

 mass, an outer generative or micropylar mass, and a loose 

 central tissue. On the micropylar summit of the generative 

 mass, one or two typical archegonia arise. In Casuarina each 

 of the ultimate megaspore or embryo-sac cells divides by free 

 cell formation into an antipodal set of four cells and an outer 

 or micropylar set of four. From their future relation and 

 behavior the writer would consider that each set of four rep- 

 resents a divided up prothallial mass, which bears one rudi- 

 mentary archegonium that forms sex-cells. This view however 

 he sets forth Tvith much reserve, and would await future com- 

 parative studies of the species in both genera. 



In some species of Ephedra, and also in Casuarinay the seed 

 is surrounded by firm bract leaves that form a protection to 

 the "fruit." 



The above remarkable points of fundamental agreement 

 between Ephedra and Casuarina seem amply to warrant the 

 conclusion that the latter has evolved through an ancestry 

 that was closely related to Ephedra, though partaking of 

 some characters that lean toward Gnetum. Further we would 

 regard Ephedra as semi-angiospermic, in that the tenninal 

 lobes of the carpels do not fuse to form stigmas, and that this 

 fusion in Casuarina constitutes it angiospermic, though the 

 stylar cylinder in it points to a more primitive semi-angio- 

 spermic state. Casuarina then would stand as a unique genus 



