202 STUDIES IN CRYPTOGAMS 



and, since the zygospore germinates directly into a new gametophyte, 

 there is probably no sporophyte. In some other algae traces of a sporo- 

 phyte have been found, but the discussion of these would lead too far 

 for the present purpose. 



In the ferns the egg-cells are developed on the prothallus. This 

 then is the gametophyte. It corresponds to the thallus of marchantia 

 and to the "moss plant," but it has become much reduced. The plant 

 developing from the fertilized egg-cell is the large and beautiful "fern 

 plant" differentiated into stems and leaves. Since the fern plant 

 produces the spores directly, it is the sporophyte and corresponds 

 to the shaft and capsule of the mosses. Both sporophyte and gameto- 

 phyte lead an independent existence. 



As we pass on to equisetum and oscetes, the sporophyte is still 

 more conspicuous in comparison with the gametophyte. In isoetes the 

 prothallus (gametophyte) is very rudimentary, consisting only of a 

 few cells remaining within the spore, which merely bursts to expose 

 the archegonia or to allow the sperm-cells to escape. Moreover, the 

 spores have become differentiated into micro- and macrospores corre- 

 sponding to the pollen and embryo-sac of higher plants. 



This gradual increase of the sporophyte and reduction of the gameto- 

 phyte can be traced on through the flowering plants in which "the 

 plant" is the sporophyte, and the gametophyte is represented simply 

 by a few cells in the germinating pollen grain, and in the embryo-sac. 



