XXIV.] INSTANCES OP RUNNING OUT. 379 



tics. These are instances in which change of soil 

 causes running out. Climate exerts a wonderful 

 effect upon vegetation. Transfer northward dwarfs 

 plants and induces coordinate changes. Dent corn 

 taken far north after a time becomes flint, as has 

 been shown by the experiments of Beal and others. 

 And Beal observes* that in southern Michigan dent 

 "ears grow shorter, kernels become shorter and 

 rounder at the ends." Some plants possess a 

 strong tendency towards variation which appears to 

 be in a measure independent of surroundings. The 

 tomato is a good example ; varieties do not long 

 retain their original characters. It is probably im- 

 possible to find in the market to-day the Tilden 

 tomato, as it was known when the variety first 

 appeared ; and the Trophy has changed consider- 

 ably from its original character. In short, the very 

 fact that we can improve varieties by good cultiva- 

 tion, and that we are enabled to obtain new varieties 

 at all, are indubitable proofs that varieties run out. 

 Upon these facts depends all possibility of advance in 

 the origination of varieties. And upon this general 

 law, also, hangs the whole framework of evolution. 



Bud -variation comprises all change which comes 

 through the agency of grafts, cuttings and tubers. 

 By graftage or cuttage we simply multiply the orig- 

 inal plant, — we do not take offspring from it, — and 

 we have every reason to expect, what all observation 

 shows, that propagation by buds should give a less 

 variable result than propagation by seeds. And yet 

 there are instances in which plants do not ' ' come 

 true" from cuttings or grafts. As a philosophical 



• Rep. Mich. Bd. Agr. 1876, 113. Quoted in Essay XIX. 



