THE HOMOSPOROUS LEPTOSPORANGIATJE 



347 



germinated spore has an exceedingly delicate endospore, which 

 is difficult to demonstrate, but after the exospore bursts along 

 the three ventral ridges, and the endospore is exposed, it be- 

 comes very evident. 



The first division takes place after the spore has elongated 

 slightly, and is usually transverse, separating the small rhizoid 



FIG. 191. Osmunda Claytoniana. A, Ungerminated spore; i, ventral surface; 2 t 

 optical section, Xsso; B, germinating spores, X27S; r, primary rhizoid; C-E, older 

 stages, X275; sp, spore membrane; x, apical cell. 



from the large prothallial cell (Fig. 191, B). The young rhi- 

 zoid contains chlorophyll, but not so much as the larger cell. 

 As germination proceeds the chloroplasts separate and increase 

 in size. They are often arranged in lines extending from the 

 large nucleus to the periphery of the cell. As a general thing,, 



