382 COOK 



The opinion has long existed among horticulturists that varie- 

 ties of fruit trees tend to deteriorate, but a biological explana- 

 tion has been lacking thus far. The most prominent horticul- 

 tural writer to defend such a view is Burbidge, who holds that 

 budding and grafting are artificial and unnatural processes, for 

 which propagation by rooted cuttings should be substituted. 

 The analogy of the seedless tropical root-crops indicates that 

 the use of cuttings would afford no protection against the grad- 

 ual reduction of fertility, though the suppression of seeds in 

 fruit trees may not be an undesirable symptom, except when it 

 is accompanied by a deterioradon in quality. Only a few hor- 

 ticultural varieties have been propagated as clones for more than 

 a century, but the advance of sterility has already become ap- 

 preciable to nurserymen, who are careful to plant seeds from 

 seedling trees, in the belief that these germinate better and pro- 

 duce more vigorous stocks than the fruit of grafted clonic 

 varieties. 



That superior varieties are commonly deficient in vigor is thus 

 explainable without reference to any special perversity of nature ; 

 such varieties may owe their reproductive debility to the fact 

 that they have been more carefully and persistently propagated 

 without crossing. Some varieties of peaches, for example, 

 yield a very small percentage of viable seed. In France many 

 attempts to secure seedlings of the "Alexander" have failed. 

 This variety and the very similar " Amsden " appeared about 

 the same time and are supposed to be seedlings of " Hale's 

 Early," a variety also notably deficient in reproductive fertility, 

 since only about ten per cent, of the seeds germinate. The 

 seedlings of " Hale's Early" are also, as a general rule, very 

 diverse, without close resemblance to the parent or to each other. 

 The variety called " Hill's Chili " affords an instructive contrast, 

 in that practically all the seeds germinate and about ninety per 

 cent, of the seedlings come true to the parental type, leaving 

 about ten per cent, of variations. 1 



Obviously, the evolutionary status of these two varieties is 

 very different ; one is entering upon the stage of mutative aber- 



'For these interesting facts I am indebted to Mr. William A. Taylor, of the 

 United States Department of Agriculture. 



