256 THE CULTURE OF FARM CROPS. 



grains escape. They either fall upon the adjacent stigma," 

 or are carried to it by insects, to whom the pollen grains 

 adhere by their points or their viscidity, and who are in 

 pursuit of honey. Or they are blown by the winds and fall 

 upon the stigma, and adhere to it by means of a viscid fluid 

 which exudes from it. 



The grain of pollen which falls upon the stigma imme- 

 diately begins a process of growth. It sends out a prolonga- 

 tion of its inner coat, which is extremely thin and delicate, 

 into the soft substance of the stigma, and through the inte- 

 rior of the style into the ovary; just as the slender rootlet 

 from a seed sinks into the soil. It then penetrates the ori- 

 fice of the ovule, and reaches the embryo, when it discharges 

 a portion of the soft pulpy mass which becomes the germ of 

 the embryo. 



THE GERM consists of a vesicle or cell, which has a very 

 delicate membranous coat or envelope in which there are a 

 small quantity of mucilaginous fluid, some minute grains, 

 and a soft pulpy mass called the nucleus. 



Thus we have now traced the whole process of plant 

 growth, and the structural development from its original 

 cell to the final accomplishment of its purpose, which is seen 

 to be the reproduction of this original cell, enormously in- 

 creased in number; some plants producing many millions of 

 seeds and such cells. And we have returned to this rudi- 

 mentary cell, with its albuminous germ imbedded in the 

 starch, which is formed in the substance of the seed, as will 

 be explained in the following chapter. 



It may be asked, however, at this point, how and by what 

 general natural provision the perpetuation of species is ef- 

 fected; and how a destructive mixture of kinds is avoided 

 when this diffusion of pollen is so general in the atmos- 

 phere. Just here we are met with the common natural law 

 which provides that different species cannot mingle, and 

 that the foreign pollen shall be inert and unproductive. 

 Thus the pollen from a pear tree may fall upon the flowers 

 of an apple tree to any extent, but there is no reciprocal re- 

 lation or action between them; the foreign pollen grains. 



