438 



EEPEODUCTION. 



angiosperms shows that in the latter the nucleus divides, but 

 that the division stops here, no true dividing-wall being formed. 

 1134. Ovule of (jymiiosperms. Ttie 

 ovule is always ortliotropous. It has an 

 integument which is sometimes prolonged 

 so as to form a flesly tube communicating 

 with the nucellus. 



The nucellus, like that of angiosperms, 

 contains an embryonal sac ; at an early 

 stage this is filled with endosperm, which 

 it will be remembered is not developed in 

 angiosperms until after fertilization. Some 

 of the upper cells of the endosperm are 

 rather larger than the others, elongated in 

 the direction of the axis of the ovule, and 

 each surmounted b}- a " rosette " of minute 

 cells which comes between the group and 

 the summit of the embrj'o sac. These large 

 cells, with their rosettes, are termed cor- 

 pusculea. These corpuscules are considered oospheres. Around 

 them in the embryo sac there ap- 

 pears to be nothing corresponding 

 strictl}' to the synergidas, the an- 

 tipodal cells, etc., observed in the 

 angiosperms, although some ho- 

 mologies have been pointed out. 



In some cases, like that figured, 

 there is a sort of depression at 

 the summit of the endosperm, 

 which has been called the pollinic 

 chamber. 



1135. Contact of pollen with 

 the ovule. As the name indi- 

 cates, the gymnosperms are naked 

 seeded ; no stigma or style inter- 

 venes between the pollen and the 

 ovule. When the divided pollen 

 of the gymnosperm falls upon the micropyle of the ovule, It 



Fig. 207. PoUen-graiii of Ceratozamia longifolia. A, grain with partial partitions ; 

 B, the same emitting its tube, ps, which has ruptured the outer coat; y, minute 

 inactive cells. (Juranyi.) 



Fig. 208. Longitudinal section of the nucellus of the naked ovule of Juniperus 

 Virginiaiia. 71, nucellus; se, membrane of the embryonal sac; c, endosperm; c, cor- 

 puscles ; p, a pollen-grain which has protruded its large tube as far as the corpuscles. 

 (Sirasburger.> 



