FERTILISATION. 



87 



At the eud of tift^'-five days after pollination the pollen-tubes had 

 penetrated the ovary in countless nunibevs, and had completely choked 

 up the canal leading from the stigniatic chamber to it, but no actual 

 impregnation of the ovulfs could be detected; the tubes lay alongside 

 tlie placentas and among the ovules, and had reached as far as the 

 bottom of the ovary. Twenty days later the ovules were not only 

 enlarged but were also undergoing a change in form, and at the end 

 of three niontlis after pollination it becan]e possible to luiderstand with 

 tolerable certainty the process by which the impregnation of the ovides 

 is effected, and to get an idea of the space of time rcipiired for its 

 accomi)lishment. 



This will be best seen by reference to Fig. 9. D E and F represent 

 two-thirds natural size three transverse sections of the ovary, D fifty-five, 

 E seventy-two, and F ninety days after the pollination of the flower ; 

 these Avith the preceding sections form a series showing the development 

 of the OA^ary at five ilifi'erent stages after the pollination of the flower. 

 The development of the rudimentary ovules 

 are also represented at the corresponding 

 periods at A B C D and E in the next 

 figure. This series simply shows the develop- 

 ment of the rudiment to the perfectly ana- 

 tropous ovule ; it is at this stage thai: 

 imi)regnation takes place. 



The pollen-tubes push down into the ovary 

 in countless innnbers, and make their way 

 along the placentas and among the protuber- 

 ances of those that bear the groups of ovules 

 in i\w manner shown in Fig. 11. The form 

 of the perfect ovule may be regarded as 

 nearly cylindric, being slightly contracted at '^ e 



the apex. The development of the im- ^^"' ^°' 



pregnated ovule to the mature seed is shown in tlie annexed series in 

 Fig. 12, all aliont 100 times enlarged. F is the perfect ovule, G is an 

 intermediate form lietween F and II, TI one munth older than F, and I 

 with nucleus n one month older lh;ni 11. A group of such at this 

 stage is represented in Fig. 13. The impregnated ovules h:id tlieiue attained 

 their mature form an<l size live months after the pollination of the 



