630 



PHYSIOLOGY. 



group of five, from which ultimately all the tissues of the embryo 

 are formed, recalls the single apical cell of Cryptogams, but it is 

 soon lost by subdivision. As there are several corpuscles, and 

 each produces four suspensors. a large number of rudimentary em- 

 bryos are developed ; but usually only one of all these rudiments 

 is perfected. 



That embryo which is fully developed gradually increases in 

 size, and most of the structures 

 above described disappear, so 

 that the ripe seed exhibits a sin- 

 gle embryo imbedded in a mass 

 of endosperm or albumen (fig. 

 607, D), the latter originating 

 apparently from the nucleus of 

 the ovule. The radicle is covered 

 by apileorhiza, which is intimately 

 blended with the substance of the 

 endosperm. 



The phenomena presented in other 

 Pinaceae, in Taxus, and in the Oy- 

 cadaceae agree in most of the essen- 

 tial particulars. There appear to be 



Some Curious peculiarities in the D ; Vertical section of the seed (C/a). E. 



Gnetaceae, which are not yet com- 

 pletely made out. In Welwitschia, 

 whose anomalous structure has been described at pp. 137, 363, the embryo- 

 sacs grow out of the primary embryo-sac *. 



Pinus sylvestri*. A. Carpel with two naked 

 ovules ; a, micropyle. B. Carpellary scale 

 of ripe cone, with seeds (a). C. A seed 

 separated (a), having a wing-like process 

 D. Vertical section of the seed (C, a). 

 Young plant from germinated seed. 



Ovules of A.ngiospermia. 



The early history of the ovules of this group is analogous to 

 that of the ovules of Gymnosperms, excepting in the particular 

 that they arise from the placentas existing in closed ovaries in- 

 stead of being developed upon the exposed surfaces of open carpels. 



The ovules arise from the placentas as minute cellular papillae 

 (fig. 608), which gradually take form, and exhibit the regions and the 

 modifications of their arrangement described in an earlier section. 



The annexed drawing (fig. 609) actual views, drawn to a scale, of the 

 development of the minute ovules of Orchis illustrates the gradual for- 

 mation of the coats, &c. Fig. C09, a, represents a young ovule projecting 

 out from the placenta, before it has become anatropous ; the nucleus here 

 consists merely of the embryo-sac surrounded by a single layer of cells, 



* For further details, which the restrictions imposed by the size of this 

 volume forbid us to enter upon, the student should consult Strasburger's 

 'Befruchtung bei den Coniferen,' his ' Coniferen und Gnetaceen,' and especially 

 his treatise ' Zellbildung und Zelltheilung.' 



