iqo8] 



YAMANOUCHI—APOGAMY IN NEPHROD1UM 



299 



developed. The central cell, when it remains undivided, grows to a 

 considerable size, with a corresponding increase in the size of its 

 nucleus, which finally assumes a form similar to that of an egg, but 

 it always appears collapsed. When canal cells and egg are formed, 

 they also appear collapsed. The collapsed appearance of the cen- 

 tral, canal, and egg cells is likely induced by the artificial treatment 

 of the prothallia rather than by fixing reagents. 



Whether the egg in 

 such a collapsed con- 

 dition is still capable 

 of fertilization, is ques- 

 tionable, but the writer 

 is inclined to believe 

 that it is incapable of 

 functioning. No case 

 of a sperm having 

 entered an egg was 

 found. 



Not only is the 

 formation of arche- 

 gonia extremely rare, 

 but when formed they 

 are very much belated. 

 In all cases in which 



Fig. i. — Two sections of apogamous prothallia, 

 showing two different stages in the development of 

 archegonia; the shaded regions represent sporophytic 

 outgrowths; a, archegonium with central cell; b, 

 archegonium with canal cells and egg. 



their formation was observed, apogamous sporophytic outgrowths were 

 already in an advanced stage of development (figs, ia, b). Hence 

 it is reasonable to suppose that in the apogamous prothallia a tend- 

 ency to develop sporophytic outgrowths becomes predominant when 

 the power of forming archegonia becomes weak. 



SPOROPHYTIC OUTGROWTHS 



As described before, during the early development of prothallia, 

 mitoses occur in the vegetative cells just as in normal prothallia, 

 except that the mitotic figures are comparatively large. The mitoses 

 continue in the vegetative cells and there are organized prothallia of 

 a single cell layer in thickness. The general outline of the prothallia 

 does not show any peculiarities which might be regarded as charac- 

 teristic of apogamous prothallia as distinct from normal ones. 



