'260 Principles of Plant C'ulture. 



the most desirable individual plants of each species were 

 protected and multiplied, or at least were permitted to 

 perpetuate themselves. Since the offspring tends to re- 

 semble the parent (18), the persistent propagation from 

 the best has resulted in more or less marked improve- 

 ment. Chance crossings have aided the process (t45). 

 These facts furnish hints for the further improvement of 

 plants. 



434. The Variability of plants Renders their Improve- 

 ment Possible. In a species of which the individual 

 plants are all practically alike, as in many wild plants, 

 we can do little in the way of plant breeding, except to 

 give treatment that promotes ^'ariability. la a species 

 in which the individuals manifest different qualities, 

 how^ever, we may hope to secure imjjrovement by using 

 the most desirable plants as parents from which to secure 

 still further variability. 



435. Variations are Not Always Permanent. If we find 

 a chance seedling of the wild blackberry, for example, 

 that has remarkably fine fruit, the plants grown from 

 seeds of this fruit are not always equal in quality to the 

 parent. The tendency, in such cases, is for the seedling 

 plants to revert or go back to the ordinary type of the 

 species, and the more marked the variation, the stronger 

 is the tendency to reversion. 



436. How to Fix Desirable Variations. A fixed varia- 

 tion, i. e., a variation of which the progeny resembles the 

 parent in all important characters, becomes a variety (21)* 

 as this word is used -o'ith reference to cultivated plants. 



* Varieties tliat reproduce ttieir more important characters wlien 

 grown from seed, are often called raff.';. 



