272 Principles of Plant Culture. 



guarded, and when the art of propagation became known, 

 these plants were most multiplied. In each successive 

 generation, 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 resemble the parent (18), the persistent propa- 

 gation from the best has resulted in more or less marked 

 improvement. Chance crossings have aided the process 

 (445). These facts furnish hints for the further im- 

 provement of plants. 



434. The Variability of plants Renders their Im- 

 provement Possible. In a species of which the indi- 

 vidual 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 variability. In 

 a species in which the individuals manifest different 

 qualities, however, we may hope to secure improvement 

 by using the more 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 ex- 

 ample, 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 

 variation, i. e., a variation of which the progeny resem- 

 bles the parent in all important characters, becomes a 



