SEEDS 



351 



whilst the radicle (r.) arises as a pointed structure at the opposite 

 end, adjacent to the suspensor (5.). The number of cotyledons 

 is very variable ; there are only two in Taxus and Cupressinece 

 (Fig. 195, B), whilst in Pinus (Fig. 195, A) there are from three 

 to seventeen, according to the species. 



As the embryo enlarges it absorbs the food-reserves stored 



G. 



FIG. 204. Pollen and embryology of Pinus. A, Mature pollen grain 

 in which the nucleus has not yet divided ; B, pollen grain at the 

 time of pollination ; C, lower end of pollen tube a little before fertilisa- 

 tion, a.c., antheridial cell ; s.c., stalk cell ; t.n., tube nucleus ; v.c., 

 vegetative cell; w., wing of pollen grain; (in C), the two male 

 nuclei. D-G, Embryology. D, Fertilised ovum, with the nucleus 

 divided into four : E, lower end of oospore, showing the young pro- 

 embryo ; F, much older proembryo ; G, almost mature embryo. 

 cot., cotyledon ; em., embryo ; p., plumule ; r., radicle ; 5., suspensor. 

 (A-D after Ferguson ; the remainder after Strasburger.) 



up in the prothallus and gradually displaces it. At the time 

 when the seed is fully mature, however, a considerable part of 

 this tissue still persists unaltered around the embryo and con- 

 stitutes the endosperm (Fig. 205, A, e) ; the seed of Conifers is thus 

 albuminous. The food-reserve is largely of the nature of oil, and 



