Mosses, Ferns, and Horsetails. 



297 



they are neither more nor less than the sporophyte 

 parasitic upon the gametophyte. 



We see that in pro- 

 ceeding from the moss 

 to the fern, or from a 

 lower to a higher type 

 of vegetation, the ga- 

 metophyte becomes 

 much reduced in size 

 and complexity of 

 structure, while the 

 sporophyte relatively 

 advances in these re- 

 spects (compare shaded 

 and unshaded portions 

 of Figs. 157-158). 

 Turning now to the 

 Spermatophy tes or flow- 

 ering plants, the most 

 complex and special- 

 ized of plants, and the 

 latest product of plant 

 evolution, we find two 

 kinds of spores (read 

 paragraph 142, page 

 201), the pollen spores 

 and the embryo sac 

 spore within the ovule. 

 The fact that the em- 

 bryo sac is a spore is 

 not so evident from its appearance as from its behavior. 



In tracing the life cycle of a fern and a moss we began 

 with the germination of the spores, and we shall begin at 



FIG. 159. 



Diagrams of the sporophyte and gametophytes 

 of a flowering plant. The pollen spore (d) 

 produced asexually on the plant (sporophyte) 

 is the beginning of the male gametophyte, and 

 the embryo sac spore m, also produced asexu- 

 ally on the sporophyte, is the beginning of 

 the female gametophyte. All of both gameto- 

 phytes (e and n) produced by the germination 

 of both kinds of spores is shaded ; all of the 

 sporophyte is left unshaded. There is no dif- 

 ferentiated archegonium and antheridium on 

 the gametophytes. b and c, later stages than 

 a. The young sporophyte or embryo (0) 

 has sprung from the fertilized egg. At/ is the 

 endosperm. 



