146 STUDY OF COMMON PLANTS. 



with that of the ferns. In both classes the germinating 

 spore gives rise to a prothallium, ■ — a flat, cellular structure 

 on which the archegonia and antheridia are produced. 

 This is the oophyte, or sexual generation. The leafy- 

 plant succeeds this, arising from the development of the 

 fertilized oosphere, and constitutes the sporophyte or non- 

 sexual generation. 



Selaginella and its allies, which represent a rather hetero- 

 geneous group of the higher cryptogams, including club- 

 mosses, quillworts, and some others, are also 

 characterized by alternation of the oophyte, or 

 sexual generation, with the sporophyte, or non-sexual gen- 

 eration. The latter differs widely from that of the ferns 

 and horsetails, in that instead of one kind of spore, giving 

 rise to a prothallium which bears both antheridia and 

 archegonia, there are two kinds, macrospores, or female 

 (archegonia-bearing) spores, and microspores, or male 

 (antheridia-bearing) spores, — a distinct foreshadowing of 

 what is seen in flowering plants, — the microspores corre- 

 sponding to pollen-grains, and the macrospores to the 

 embryo-sac of the ovule. The oophyte, again, as compared 

 with that of the ferns, is reduced in size, and all its early 

 stages of development are completed ivithin the spore, 

 reminding us of similar facts in the developmental history 

 of phanerogams. The prothallium of the microspore, in par- 

 ticular, is reduced to the lowest terms, and should be com- 

 pared with the vegetative cells (rudimentary prothallium) 

 in the pollen-grain of certain gymnosperms. 



The facts thus briefly summarized require far more time 

 than is at our disposal for their complete demonstration. 

 Progressive ^^ut in any case it is plain that in our study of 

 tnra^^on cryptogamous plants, we have been passing suc- 

 origin. cessivcly from lower to higher forms, a fact that 



