THE STANDPOINT OF BOTANY 69 



The same kind of progressive change is shown 

 also in the embryo of Gymnosperms. In the 

 most primitive condition, the first stage of em- 

 bryo formation is extensive free nuclear division 

 within the fertilized egg; after this, walls are 

 formed and the egg becomes filled with tissue, 

 the proembryo. Throughout the Gymnosperm 

 series there is a steady reduction of the amount 

 of free nuclear division, and with it a reduction 

 of the amount of proembryonic tissue, so that 

 finally it occupies a very small portion of the f er- 

 tihzed egg. All this change has taken place fur- 

 ther from outside influences than the change in 

 the gametophyte, for the embryo is imbedded in 

 the gametophyte. 



It may be claimed that these are not the char- 

 acters that taxonomists use in distinguishing spe- 

 cies. This is true, but they are just the charac- 

 ters that distinguish great groups, and represent 

 the advancement of the plant kingdom as a whole. 

 It so happens that both of the progressive 

 changes noted as occurring among Gymnosperms 

 culminate among Angiosperms. 



The male gametophyte of Gymnosperms 

 shows a similar progressive change, not so steady, 

 but none the less evident. Its few cells are con- 

 tained within the resistant wall of the pollen 

 grain which produces it. In the more primitive 

 condition the vegetative cells are variable in nimi- 

 ber, but evident; but there is a persistent tend- 

 ency to ehminate them, which reaches comple- 



