1908] 



YAMANOUCHI— APOGAMY IN NEPHRODIUM 



301 



established in a certain region of the superficial layer a group of 

 parallel cells. The increase of the superficial cell is remarkable in 

 apogamous prothallia. 

 In ordinary prothallia, 

 if such a growth in size 

 ever occurs in a super- 

 ficial cell of the cushion 

 region, it is an arche- 

 gonium initial; how- 

 ever, the archegonium 

 initial never attains 

 such conspicuous de- 

 velopment, surpassing 

 all the other superficial cells in that region. Moreover, the development 

 of the archegonium generally occurs after the cushion region has ex- 

 tended over a comparatively large area and attained some thickness. 

 On the other hand, the increase in size of the superficial cell in an 



Fig. 2. — Two sections of normal prothallia, showing 

 different stages in the development of archegonia. 



ff h 



Fig. 3. — Eight successive sections of the same apogamous prothallium showing 

 a single superficial growing to considerable size in a young cushion. 



apogamous prothallium commences at an early stage and is associated 

 with the gradual formation of the cushion. The accompanying figures 

 will illustrate the situation. In fig. 2, a, b is shown the cushion region, 

 displaying different stages of archegonium development in normal 

 prothallia. Fig. 3 represents eight successive sections of the same 



