How Domestic Varieties Originate 231 



the normal type, the greater, in general, is the likeli- 

 hood that it will be perpetuated, although this may 

 not be true of sports. This is admirably illustrated in 

 crosses. The seed-progeny of crosses between closely 

 related varieties, or between different plants of the same 

 variety, is more uniform and usually more easy of improve- 

 ment by selection than the progeny of hybrids. In un- 

 crossed plants, the general tendency is to resemble their 

 parents, and the greater the number of like ancestors, 

 the greater is the tendency to "come true." There is 

 thought to be a tendency, though necessarily a weak 

 one, to return to some particular ancestor, or to "date 

 back." This is known as atavism. The so-called ata- 

 vistic forms are likely to be unstable, to break up into 

 numerous forms, or to return more or less completely to 

 the type of the main line of the ancestry. The following 

 statements touching some of the relations of atavism to 

 the amelioration of plants are the results of an excellent 

 study of heredity in lupines by Louis Leveque de Vil- 

 morin : 



"1. The tendency to resemble its parents is generally 

 the strongest tendency in any plant; 



"2. But it is notably impaired as it comes into conflict 

 with the tendency to resemble the general line of its 

 ancestry. 



"3. This latter tendency, or atavism, is constant, 

 though not strong, and scarcely becomes impaired by the 

 intervention of a series of generations in which no rever- 

 sion has taken place. 



"4. The tendency to resemble a near progenitor (only 

 two or three generations removed), on the other hand, is 



