202 PLANT-BREEDING 



the purpose of illustration only. The fruit-grower and the 

 amateur cultivator of garden plants are quite satisfied with 

 the visible qualities of their new varieties, and the question 

 as to their origin has, as a rule, but small interest for them. 

 It is to the personal kindness of Burbank that I am indebted 

 for most of the details concerning the scientific side of his 

 cultures, and, of course, my visits were too short to touch 

 upon all the questions exciting a similar interest. 



It seems to me a fact of high scientific significance that 

 combinations of characters can be obtained by crosses in 

 almost all the arbitrarily chosen directions or degrees, but 

 that new character-units are either never produced or at 

 least so rarely that an artificial origin is hardly beyond legiti- 

 mate doubt. Concerning the combinations of characters, 

 the investigators of the last decade have discovered dis- 

 tinct laws which, however, in large part, are related to 

 varietal marks. Real specific differences must, of course, 

 also obey distinct laws in their combinations, and the in- 

 variability of some of Burbank' s hybrids, as for example the 

 primus-berry, shows these laws to be more narrowly cir- 

 cumscribed than is usually assumed. 



C. HYBRIDIZATION AND SELECTION 



Apart from the clear and simple cases we have dealt with 

 in our last lecture, the ordinary aim of the hybridizer is to 

 upset the constancy of his plants, and to bring them into a 

 state of unstable equilibrium which in the end will result in 

 an extreme chaos of forms. From this chaos, he makes 

 his selections, and if they do not at once comply with his 

 wishes, he continues his crossings in order to widen still 

 more his range of types. In doing so, he is careless about the 

 real source of the improvements he obtains. ,He knows 

 the origin of his groups and strains, but rarely that of their 

 single constituents. Or, to put it into a simple phrase, if 



