194 



MORPHOLOG Y. 



393. 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 241-243 give the details. There 

 are many microspores in a single small spore-case, but 3-4 ma- 

 crospores in a large spore-case. 



394. 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. 244. Here we see that 



Fig. 244- 

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

 moved to show small prothallial cell below ; 3d, mature male prothallium still within the 

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

 three sperm cells within ; 5th 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. 



395. 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 



