CRYPTOGAMS 357 



The analogies between the sequence of alternations in the 

 two classes will be made clearer by a comparison of the 

 accompanying diagrams. The corresponding terms applietl 

 to the various organs stand in the same vertical row. Dia- 

 gram (1) shows the process as it takes place in the more 

 highly developed Pteridophytes ; diagram (2) the corre- 

 sponding phases in angiosperms. 



PTERIDOPHYTES 



<m.ospl >mic >mo > anG * ant >mg vv 

 ybos >S 

 Mospl >Mgc >Mo >arG y arc > fg f^ 



mospl, micTOsporophyll ; mic, microsporangium ; mo, microspores ; anG, male 

 gamctophyte ; ant, antheridia ; 7ng, antherozoids. The letters in the lower line 

 stand for the corresponding female organs. 



SPERMATOPHYTES 





■2Ml ^/c — -> »io'— - 



de veloped 



, de veloped 

 .em ^end 37,;^,— 



gymno 

 sperms 



st, stamen ; an, anther ; pol, pollen ; fc, food cells in pollen grain ; gc, generative 

 cell ; p, pistil ; ov, ovules ; cm, embryo sac ; end, endosperm ; ec, egg cell. 



415. Disappearance of the gametophyte. — The seed is a 

 comparatively recent development in plant evolution. It 

 has no counterpart anywhere among the cryptogams, but is 

 strictly characteristic of the three great orders of Spermo- 

 phytes: Monocotyl, Dicotyl, and Gymnosperms, which 

 compose the greater part of the vegetation of the globe. 

 Structurally, it is a matured sporangium containing a rudi- 

 mentary sporophyte (the embryo), and a reduced gameto- 

 phyte (the embrj^o sac), which, under the form of endosperm, 

 has dwindled to an insignificance that makes it difficult to 

 recognize it as a phase in an alternation of generations. 



416. Significance of the sporophyte. — The gametophyte 

 is obviously a more ancient and primitive structure than the 

 sporophyte, which first becomes prominent in the ferns and 



