2 20 PLANT-BREEDING 



attached by the practical breeder to the purity of his fer- 

 tiUzations. Of course, in scientific investigations, the father 

 is of equal importance with the mother, and the utmost care 

 has to be taken that the stigma is covered with pure pollen. 

 Moreover, in the pedigree, the hnes of the male ancestors 

 require the same care as the female line. Exact and elaborate 

 book-keeping is the rule, and no single polHnation should 

 be made that is not thoroughly controlled and registered. 



In practice, however, such a susceptibility would be as 

 impossible as useless. The proof of the pecHgree is not the 

 aim of the experimenter. He only looks for the result. In 

 crossing six or seven species and hundreds of their hybrids, 

 the pollen is brought from one flower to the other, as oppor- 

 tunity is offered. Hundreds of crossings may be made in a 

 few hours, and their seed may be saved in mixture without 

 special care, or too much loss of time. If, however, each of 

 these crosses has to be kept separate, to be labeled and 

 registered, and its seed sown apart from the others, the 

 amount of work will increase a hundred-fold without any 

 chance of giving more or more profitable hybrids. 



Separate pedigree book-keeping being thus impossible, 

 small impurities of the pollen cannot be avoided and are not 

 to be noticed. Pollen is brought by the finger to the stigma, 

 but a breeder would simply laugh at the idea of a scientific 

 investigator washing his hands between successive polhna- 

 tions, or inspecting his fingers with a lens in order to remove 

 some stray remaining pollen grains Quite on the contrary, 

 such unintentional crosses often bring greater chances of 

 unexpected success than the regular and contemplated pollin- 

 ations, and if, perchance, they give hybrids of inferior quahty, 

 the damage is only small, since the offspring is sure to be 

 eliminated bv the next selection. Thus we see that some 

 freedom must be allowed in the choice and in the purity of 

 the pollen. But, on the other hand, it is easily seen that much 



