METHODS 



33 



Morkia in the character of the foot, which is somewhat bulbous, while in 

 P. radiculosa the foot is pointed and merges more or less gradually into 

 the seta. P. Levieri is somewhat intermediate between P. Zollingeri and 

 P. radiculosa in the form of the foot. 



Fig. 19. 



A. Section of a young sporophyte of P. Zollingeri, in which the young spore 



mother-cells and elaters are differentiated; x 25. 



B. Part of the sporogenous region, showing spore-mother cells, sp, and young 



elaters, el. 



C. Foot of the sporophyte. 



D. E. Young sporophytes of P. Levieri, x 25. In E there was a second abortive 



sporophyte, sp 2 , within the calyptra. 



As the capsule develops the wall becomes clearly delimited from the 

 sporogenous tissue within. The wall is composed of about three layers 

 of cells throughout most of its extent. In P. Zollingeri (Fig. 18, C) the 

 wall is three-layered also, or sometimes four-layered at the apex, the outer 

 layer having the cells conspicuously larger than the two inner layers. In 

 P. radiculosa (Fig. 21, A) the wall at the apex of the capsule is much 

 thicker, and forms a conspicuous beak. P. Levieri is intermediate in this 

 respect also between P. Zollingeri and P. radiculosa. 



The sporogenous tissue in P. Zollingeri forms at first a somewhat 



