1 66 Introduction to Botany. 



ovule contains a large cell, or spore (z), which produces the 

 egg, and is therefore necessary to the production of seed. 



The flower may be lacking in both calyx and corolla, but 

 if it have stamens and pistil, or only pistil, provided pollen 

 is brought to it from some other flower of the same kind of 

 plant, it may still bear seed. For this reason the stamens 

 and pistil are called the essential parts of the flower. 



That portion of the flower from which the calyx, corolla, 

 stamens, and pistil spring is called the 7'eceptacle (a). 



120. Process of Fertilization. — In order that the fertili- 

 zation of the egg may take place, the sperm from the 

 pollen must reach the egg in the ovule, which in most 

 cases is entirely shut off from the exterior world by the 

 walls of the ovary. We can see that in this case it would 

 avail little for the sperm to be motile from plant to plant, 

 as in the case of Oedogonium, for it would have to pass 

 through the air, instead of through water, and would be 

 carried rather by the winds than by its own motion. The 

 process of the transference of the sperm has therefore 

 been modified to meet the aerial environment. The 

 anthers burst open, and the liberated pollen is then blown 

 about by the wind, or is carried from flower to flower by 

 insects which are seeking nectar or pollen for food for 

 themselves or their young; or in some cases the anthers 

 may touch the stigmas and transfer to them their pollen, 

 or the pollen may drop from the anthers upon the stigmas ; 

 while in water plants it may be carried to its destination by 

 means of movements of the water. 



After the pollen has been transferred to the stigma (as 

 at m, Fig. 88) it imbibes moisture from the moist and sugary 

 stigmatic surface, and increases in size so that finally the 

 inner membrane (represented by the innermost line of 

 the pollen case) pushes through the outer coat (thick, and 



