438 The Living Plant 



to the female cell in the ovule. Now in nature this transfer is 

 effected by the agency of wind, water, or insects, but in culti- 

 vation man can transfer the pollen himself if he pleases, and 

 can thus to some extent control the parentage of the new in- 

 dividuals formed in the ovules. And these are the various com- 

 binations he can make : 



(1) He can pollinate a given stigma by pollen from the same 

 flower. This is called close pollination in Botany and in-breeding 

 in Horticulture. With many plants, perhaps the majority, no 

 result follows, for the seed does not set, the ovule being sterile to 

 the pollen of the same flower; while in many kinds of flowers such 

 pollination is impossible, because the pollen and ovules in each 

 single flower ripen at different tunes, or because of other im- 

 pediments. It is thus obvious that nature takes trouble, so to 

 speak, to prevent such in-breeding; and the implication that such 

 breeding is in general not advantageous is confirmed by such 

 evidence from experiment as we possess, which shows that the 

 offspring of close in-breeding are generally inferior in variability 

 if not in vigor to those more widely bred. But in the very fact 

 that in-breeding does not favor variability is found its chief horti- 

 cultural importance, for it can be used to keep a race true to its 

 type when that is desirable. In practice, however, such use is 

 very limited because the same result can be attained much more 

 easily in most plants by propagation through cuttings or grafting, 

 and by the systematic weeding out of all plants (horticulturally 

 called "rogues") which show individual variations. 



(2) He can pollinate a given stigma by pollen from another 

 flower on the same plant. This also is in-breeding, and experi- 

 ments have shown that the results are little if any better than in 

 the case of the first method. 



(3) He can pollinate a given stigma by pollen from a different 

 plant of the same kind. This is called cross pollination in Botany, 

 and crossing in Horticulture, and is that to which most of the 

 cross-pollinating mechanisms and methods in flowers are adapted. 



