FURTHER STUDTES OA' G VMJVOSPERAfS. 



In comparing the female prothallium of the gj'ranosperms with that of (he 

 fern group we .st;e a remarkable change has taken place. The female pro- 

 thallium of the gymno- 

 Es -J^ p sperms is very much 



j\ « 1 I ^_.^^^ reduced in size. Espe- 



cially, it no longer leads 

 an independent existence 

 from the sporophyte, as 

 is the case with nearly 

 all the fern group. It 

 remains enclosed within 

 the maerosporangium (in 

 cvcas if not fertilized it 

 somii-limi^s grows outside 

 o[ tlie maerosporangium 

 and becomes green), and 

 derives its nourishment 

 through it from the sporo- 

 phyte, to which the latter 

 remains organically con- 

 nected. This condition 

 of the female prothallium 

 of the gymnosperms 

 fig' 374- necessitated a special 



Gingko biloba. --J, mature pollen grain ; /^.germinating adaptation of the male 



pollen grain, the branched tube entering among the cells *i ir ■ i *i ■. 



of the micellus; /:>, exhie (outer wall of f pore) ; J\, pro- prothallllira in order that 



thallial cell ; /-'.,■ aiitheridial cell (divides later to form stalk the sperm cells ma\" reach 

 ell and generative cell) ; /'g. \'egetat'\-e cell ; / '^i. \'acuoles ; 



JVc, nucellus. (After drawings by Hirase and Ikenf).) 



and fertilize the egg cell. 



Gingko biloba, diagrammatic representation of the relat'on of pollen tube to the arche- 

 goniuni in the end of the nucellus. //. p<..llen tube: .>. archegoniuni. (After drawing by 

 Hirase and Ikeno.) 



636. Gymnosperms are naked seed plants. — Thu pine, as wi; liavc seen, 

 has nal<ed seeds. That is, the seeds are iidl entbised witliiii llie carpel, l.iut 



