LITTLE CLUB MOSSES. 287 



585. Sporangia. On examining the fruiting spike, we find 

 as in lycopodium that there is but a single sporangium in the 

 axil of a fertile leaf. But we see that they are of two different 

 kinds, small ones in the axils of the upper leaves, and large ones 

 in the axils of a few of the lower leaves of the spike. The micro- 

 spores are borne in the smaller spore -cases and the macrospores 

 in the larger ones. Figures 329-331 give the details. There 

 are many microspores in a single small spore-case, but 34 ma- 

 crospores in a large spore-case. 



586. Male prothallia. The prothallia of selaginella are much 

 reduced structures. The microspores when mature are already 

 divided into two cells. When they grow into the mature pro- 

 thallium a few more cells are formed, and some of the inner ones 

 form the spermatozoids, as seen in fig. 332. Here we see that 



Fig. 33 2. 



Details of microspore and male prothallium of selaginella ; ist, microspore ; 2d, wall re- 

 moved to show small prothallial cell below ; id, mature male prothallium still within the 

 wall ; 4th, small cell below is the prothallial cell, the remainder is antheridium with wall and 

 four sperm cells within ; sth spermatozoid. After Beliaieff and Pfeffer. 



the antheridium itself is larger than the prothallia. Only an- 

 theridia are developed on the prothallia formed from the 

 microspores, and for this reason the prothallia are called male 

 prothallia. In fact a male prothallium of selaginella is nearly 

 all antheridium, so reduced has the gametophyte become here. 



587. Female prothallia. The female prothallia are devel- 

 oped from the macrospores. The macrospores when mature have 

 a rough, thick, hard wall. The female prothallium begins to 

 develop inside of the macrospore before it leaves the sporangium. 

 The protoplasm is richer near the wall of the spore and at the 



