124 



FERTILIZATIOX. 



up, l-earing an ovule at its apex. When very young the 

 ovule is a sort of cup, the mouth of which is closed by a little 

 cord, and is turned towards the apex of t!ie ovary. From all 

 access to the dome of the ovary tl;e ovule is cut off, notwith- 

 standing its position, hy the cord which over against the ap- 

 perture of the ovule, spreads into a kind of strap. It is from 

 the poifit of the ovary e, that the stigma arises; and from 

 immediately below their origin, a short cylinder projects down 

 into the cavity of the ovary. Matters being thus arranged, 

 the pollen falls upon (he stigma, and pollen tubes are forced 

 into its tissue and gradually find their way into the cylinder; 

 at the same time the ovule lengthens, contracts at its aper- 

 ture, and is brought near (he cylinder, by the elevation of its 

 umbilical cord ; at last the strap is slipped aside, the cylinder 

 lengthens, the ovule rises, and with its aperture embraces 

 the point of the cylinder which is somewhat conical, and 

 which is thus brought into contact with the nucleus. At this 

 time tliC parts are in the position represented as in B, and if 

 cut through longitudinally as at C, they will be seen to be 

 placed in the most favorable position that can be imagined, for 

 enabling the pollen tubes to enter the foramen of the nucleus. 

 150. After the discovery of pollen tubes, and the necessity of 

 the pollen coming in contact with the moist surface of (he stig- 

 ma, in order to put them fordi, it was thought that the im- 

 pregnation of the Asclipindcae, and Orchidcae formed excep- 

 tions to the general manner of producing impregnation by 

 their emission, sin?^ nature seemed to have prevented the 



