GROUP IV. GYMXOSPERMJE. 



427 



of the embryo, one or more embryonal tubes are developed which 



grow backward along the suspensor. Picea cxcelsa departs from 



this type in that the suspensors remain coherent, bearing at their 



end the cells of the lowest tier which develope into but a single 



embryo, whereas in 



the typical Abie- 



tineae four embryos 



originate from each 



oospore (polyembry- 



ouy). Only a single 



embryo is developed 



from the oospore in 



Thuja (Cupressineae) 



and in the Taxeae. 



The cotyledons 

 vary in number : 

 one, in Ceratozamia, 

 and sometimes in 

 other Cycadaceae ; 

 two, in the Cycada- 

 ceae generally, in 

 the Cupressinese 

 generally, in the 

 Taxoidese, and in the 

 Gnetaceae ; in the 

 Cupressineae some- 

 times 3-5 ; in the 

 Abietineae 5-15. 

 The cotyledons are 

 generally epigean, 

 but they are hypo- 

 gean in the Cyca- 

 daceae. 



The growing-point 

 of the root is in all 

 cases differentiated 

 endogenously, at 

 some distance from 

 the posterior end of 



the embryo. 



FIG. 251. Germinating seeds of Pinu* Pinea : I first 

 stage, ia longitudinal section : II second stage, with pro- 

 truding radicle ; A external view ; B view after removal of 

 half the seed-coat ; C longitudinal section, without seed- 

 coat; J) transverse section, without seed-coat; I/I ger- 

 mination is here completed, the cotyledons havingexpanded, 

 and the hypocotyl elongated : seed-coat ; e endosperm ; TC 

 radicle ; c cotyledons ; y micropyle ; r red membrane (re- 

 mains of nucellus) ; * the embryo-sac. 



