GENEKAL EEVIEW OP CEYPTOGAMS. 151 



lower cryptogams there are many plants in which only 

 one of these modes of reproduction is known, the higher 

 cryptogams exhibit both, and there is, as we have already 

 noted, an alternation of the generation that produces sex- 

 ual with the one that produces non-sexual spores. Passing 

 the leading classes briefly in review, we recall in the mosses 

 the leafy plant as the part on which the sexual organs, the 

 archegonia and antheridia, are produced. It is accordingly 

 called the sexual generation, or since it produces the egg- 

 cell, or oosphere, it is also designated as the oophyte. From 

 the fertilized oosphere is developed the spore-capsule, con- 

 stituting the non-sexual generation, or sporophyte. Coming 

 to the ferns, we find the same alternation of generations, 

 but in them and in other vascular cryptogams the prothal- 

 lium on which the sexual organs are borne constitutes the 

 oophyte, and the leafy plant is the sporophyte. In Sela- 

 ginella, and related plants that produce two kinds of spores 

 the prothallium is much reduced in size, but it still consti- 

 tutes the oophyte, the leafy plant, as before, being the sporo- 

 phyte. In the flowering plants, in which the embryo-sac 

 corresponds with the macrospore of the higher cryptogams 

 and the pollen grain to the microspore, the reduction of the 

 prothallium proceeds still farther, but it still represents 

 the oophyte, while the flowering plant as a whole is the 

 sporophyte. Thus it is seen that from the ferns upwards 

 there is a gradual decrease in the prominence of the pro- 

 thallium, or oophyte, but that in all the higher plants alike, 

 whether flowering or flowerless, the same alternation of 

 oophyte and sporophyte takes place, presenting what is 

 perhaps the most striking general fact in their life history, 

 and the one that more than any other attests their relation- 

 ship; that is, their common origin.^ 



1 Cf. Saohs, History of Botany, pp. 200, 201, 



