290 



BOTANY 



this is cut through, so as to expose the inner mucilaginous tissue, and the sporo- 

 carp is placed in water, the swelling mucilage forces open the sporocarp and sets 

 free the enclosed spores. The gelatinous mass has no definite shape in Pilularia, 

 but in Marsilia it forms a thick ring, to which the sori are attached (Fig. 252, D). 



The Gametophyte 



The gametophyte in the Marsiliaceae is extremely reduced, and its 

 development may occupy but a few hours. Thus, in Marsilia vestita> 



D 



B 



FIG. 256. Marsilia vestita. A, vertical section of stem-apex (X80); L, leaf^ 

 r, roots. B, stem-apex (x 450). C, youug leaf (X 450). D, older leal. E, cross- 

 section of young stem (X 80). x, apical cell. 



the whole development of the gametophyte, under ordinary condi- 

 tions, is completed within about fifteen to twenty hours from the 

 time germination begins. Pilularia, in which the gametophyte is 

 not quite so much reduced, takes about twice as long. 



Male Gametophyte. The microspore has first cut off from it a small sterile 

 cell, which subsequently may divide again (Fig. 253). From the upper, or anthe- 

 ridial, cell, a single large antheridium, with two groups of sixteen sperm-cells, is 

 formed. Here, also, the two groups of sperm-cells are sometimes considered 

 to represent two antheridia. The sterile cells and the wall-cells of the antherid- 

 ium contain numerous starch-granules, which are also found abundantly in the 



