170 



PLANT MORPHOLOGY 



A D 



Fig. 137. Sporophyte of Riccia natatis. A, longitudinal section of nearly mature sporo- 

 phyte embedded in the gametophyte, showing spore tetrads enclosed within the calyptra; 

 B, spore mother cell; C, tetrad; D, mature spore; A, X 100; B, C, D, X500. 



C D E 



Fig. 138. Development of the embryo of Cryptomitrium tenerum, X400. A, two-celled 

 stage; B, division of lower cell; C, four-celled stage, the two lower cells giving rise to the 

 foot and seta, the two upper cells to the capsule; D, eight-celled stage; E, older stage, 

 showing differentiation of sporogenous tissue in the capsule. {After Haupt.) 



