BLASTOGENIC VARIATIONS. 187 



tributed to so-called spontaneous variability. Though 

 in individual instances it may be difficult or impossible 

 to assign any reason for the sudden appearance of such 

 " spontaneous variability/' yet various observations in- 

 cline one to believe that it is probably, after all, only a 

 special instance of variations due to changed conditions 

 of life. Thus it is noticeable that all plants which have 

 yielded bud-variations have likewise varied greatly by 

 seed. They seem, in fact, to possess an inherent varia- 

 bility. Again, almost all plants showing bud-varia- 

 tion have been highly cultivated for long periods, in 

 many soils and under different climates. On the other 

 hand, plants living under their natural conditions are 

 very rarely subject to bud-variation. In some in- 

 stances, as when all the fruit on a purple plum tree sud- 

 denly becomes yellow, or all the fruit on a double- 

 flowered almond suddenly becomes peach-like, we 

 seem to perceive a direct result of changed condi- 

 tions of life; but more often than not we are com- 

 pelled to conclude that the connection is only an indirect 

 one. 



Darwin points out * that it is " a singular and inex- 

 plicable fact that when plants vary by buds, the varia- 

 tions, though they occur with comparative rarity, are 

 often, or even generally, strongly pronounced." In 

 plants raised from seed, however, the variations are al- 

 most infinitely numerous, but their differences are gen- 

 erally slight. Bud-variations clearly seem, therefore, 

 to be true discontinuous variations, and not merely 

 exaggerated normal variations. As to the ultimate 

 cause of their production, we are as completely in the 



*L. c., i. p. 443. 



