240 BREEDING 



also from the fact that the equipment and time at 

 the disposal of the biologist, though at present abso- 

 lutely inadequate for the purpose of grappling with 

 evolution as a whole, are probably sufficient for the 

 task of efiecting such improvements in domesticated 

 races of animals and plants as may be required. 



This being the case, our next step is to deal more 

 fully with the application of Mendelian principles to 

 the practice of breeding. I have already insisted on 

 what, in my opinion, is the most important service 

 which Mendel's work has done for the science of 

 heredity, namely, the establishment of the principle 

 that the contents of the germ-cells, and not the 

 outward characteristics of the animals and plants 

 dealt with, must be our guide in breeding. 



This principle can as yet only be applied when 

 the inheritance of the characters, which are being 

 bred for, fits, or may be expected to fit, into some 

 recognised scheme of heredity, such as the Mendelian. 

 If the mode of inheritance of the character in question 

 is demonstrably not Mendelian, and does not corre- 

 spond to any of the types recognised by de Vries 

 in the vegetable kingdom, it must be carefully 

 described and, if possible, interpreted ; though the 

 latter is not important. What is urgently needed is 

 an accurate description of the various ways in which 

 the characters of domesticated animals and plants 

 are inherited. It will be time enough to interpret 

 them when our knowledge of them is a great deal 

 more perfect than it is at present. For instance, 

 there is one question of the greatest importance to 



