IV THE JUNGERMANNIACE^ 89 



mature it opens by four valves which extend its whole 

 length. 



The germination of the spores of Aneura has been studied 

 by Kny ^ in A. pahnata, and by Leitgeb "' in A. pinguis, which 

 agrees in all respects with the former. The spores, as is usual 

 in the Jungermanniaceae, have a poorly -developed exospore, 

 and contain chlorophyll when ripe. Before any divisions take 

 place, the spore enlarges to two or three times its original 

 volume, and then elongates and by repeated cross-walls forms 

 a filament of varying length. In the end cell next an inclined 

 wall arises, which is met by another nearly at right angles to it, 

 and thus the two-sided apical cell is established, and the thallus 

 gradually assumes its complete form (Fig. 40, A). 



In the other thallose anacrogynous forms, i.e. Pallavicinia 

 (Fig. 38, A), the sexual organs are borne upon the dorsal 

 surface of the ordinary shoots, usually surrounded by a sort of 

 involucre. In most of these forms the apical cell is of a 

 different type from that of Aneura, but is variable even in the 

 same species. Thus in Pallavicinia cylindrica, while the 

 commoner form is nearly wedge-shaped, appearing four-sided 

 seen from the surface, and triangular in vertical section, it may 

 approach very nearly the two-sided type (Fig. 39, C). In the 

 ordinary form four sets of segments are cut off, — dorsal and 

 ventral, as in Riccia or SpJicerocarpus, and two sets of lateral 

 ones. In Pellia calycina the apical cell shows a similar form, 

 but in P. epipJiylla (Fig. 39, D, E) another type is seen. 

 Here, while the surface view is the same as in P. calycina, 

 in vertical section the cell is nearly semicircular, i.e. here 

 there are but three sets of segments, two lateral ones and a 

 basal one extending the whole depth of the thallus, and only 

 later showing a division into ventral and dorsal cells. Probably 

 this type has been derived from the former by a gradual in- 

 crease in the size of the angle formed by the dorsal and ventral 

 walls of the apical cell, which finally became so great as to 

 practically form one plane. 



Janczewski ^ followed very carefully the development of the 

 archegonium in Pellia epipJiylla, which differs a good deal from 

 that of Aneura. The archegonia are formed in groups just 

 back of the apex, but he does not seem to have been able to 

 detect any relation between them and the segments of the 



1 Kny (l). - Leitgeb (7), vol. iii. p. 48. -^ Janczewski (i), p. 3S9. 



