300 



STRUCTURAL BOTANY 



III. DEVELOPMENT AND STRUCTURE OF THE 

 SEXUAL GENERATION (OOPHYTE) 



1. THE PROTHALLUS 



On the whole, the sexual generation of the Horsetails 

 is much like that of the Ferns, though there are many 

 differences in detail, and the mode of growth and ultimate 

 form of the prothallus are less regular in Equisetum than 



FIG. 45. Equisetum maximum; large female prothallus, seen 

 from below. I, I, lobes; a, a, arche.fronia ; r.h, root-hairs. 

 Magnified about 30 diameters. (After Buchtien.) 



in such Ferns as Aspidium. The spore begins by dividing 

 into two unequal cells, and usually the smaller of these 

 grows out into the first root-hair, while the larger gives 

 rise to the green part of the prothallus. The latter 



