POLLINATION AND FECUNDATION. 



55 



developed. These flowers do not secrete nectar, or emit any 

 odor ; from their small size, as well as from the corolla being 

 rudimentary, they are singularly inconspicuous ; consequently 

 insects do not visit them, nor could they find an entrance if 

 they did. Such flowers are, therefore, self-pollinated yet they 

 produce an abundance of seed. In several cases the young 

 capsules bury themselves beneath the ground, and the seeds 

 are there matured." (Darwin.) 



15. The pollen that has been deposited on the mature stigma 

 absorbs some of the moisture that is present, and immediately 

 germinates. The outer and more brittle layer in the covering 

 is ruptured ; the inner and more delicate layer protrudes in 

 the form of a tube (Fig. 85). This grows downward through 

 the style, absorbing nourishment from the loose tissue through 

 which it passes. It finally reaches the 

 ovule, or organ in the ovary that is to 

 become the seed. The ovule is at this 

 time an oval or roundish body — being 

 an outgrowth from a portion (the pla- 

 centa) of the interior of the ovary. It 

 is enclosed in one or two coats (integu- 

 ments) that have grown up over it from 

 the base. The integuments do not unite 

 at the top, but leave a small orifice — 

 designated by a term having this mean- 

 ing, namely, micropyle. It is through 

 the micropyle that the pollen-tube 

 passes into the interior of the ovule 

 and reaches the enlarged cell or sac 

 called the embryo-cell (Fig. 85). The 

 protoplasmic contents of the pollen- 

 grain pass into and down the pollen-tube, 

 the pollen-tube fuses with a nucleus contained in the embryo- 

 cell. This process is called Fecundation.' As a result of 

 fecundation a course of development begins which results in 



itdens 



Fig. 85. 



A nucleus from 



' The less appropriate term ' 

 books. 



fertilization " has generally been used in text- 



