Improvements Made in Plants by Man 437 



concerning the causes of variation, the two, indeed, being doubt- 

 less identical in nature. Like variations, bud sports are spon- 

 taneous and fortuitous and can be rendered more frequent by 

 cultivation; and they are hereditary through the new buds they 

 produce, though never by seeds. Everybody knows that a 

 Bartlett Pear or a Baldwin Apple can be propagated by grafting, 

 but not by the seeds, which do not produce those fruits, but just 

 plain ordinary mongrel pears and apples. Were it not for the 

 fact that most of the plants which produce bud sports can be 

 propagated by slips, or cuttings, or else by grafting (which is 

 merely a process of giving ready formed roots to slips unable to 

 make roots for themselves), it would not be possible to preserve 

 bud sports, and they would perish with the plants which produce 

 them. But those methods of propagation do permit man to 

 preserve them, to his very great advantage. 



Sports from buds, however, are not the only kind, for seed 

 sports also occur, though upon the whole they are less conspicuous 

 and important than bud sports. Among brilliantly red cardinal 

 flowers, some plants occasionally occur with pure white flowers; 

 when seeds from the white flowers are planted, they produce 

 white-flowering plants. The white cardinal flowers are typical 

 seed sports, and the fact that they propagate by seed is typ- 

 ical. Some cut-leaved trees (e. g. Wier's cut-leaf Maple), and 

 some fine varieties of fruits have also originated as seed sports. 

 Whether these trees come true to seed I do not know, and the 

 matter is not practically unportant, since they can be propagated 

 far more speedily and easily by grafting. It is obvious that seed 

 sports which propagate their characters through seeds differ in 

 no essential particular, except perhaps that of degree, from the 

 mutants, or biotypes, described in the chapter on Evolution. 



3. Crossing and Hybridization. — The reader will recall that seed- 

 formation must be preceded by fertilization, which in turn re- 

 quires that the pollen-grain containing a male cell shall be trans- 

 ferred from anthers where it is made, to a stigma giving access 



