CHAP. XII. GENEBAI RESULTS. 451 



individual plants of the same species which have 

 grown in somewhat more shady or sunny, dry or damp 

 places. Plants which have been propagated for some 

 generations under different climates or at different 

 seasons of the year transmit different constitutions to 

 their seedlings. Under such circumstances, the che- 

 mical constitution of their fluids and the nature of 

 their tissues are often modified.* Many other such 

 facts could be adduced. In short, every alteration in 

 the function of a part is probably connected with some 

 corresponding, though often quite imperceptible change 

 in structure or composition. 



Whatever affects an organism in any way, likewise 

 tends to act on its sexual elements. We see this in the 

 inheritance of newly acquired modifications, such as 

 those from the increased use or disuse of a part, and 

 even from mutilations if followed by disease.f We 

 have abundant evidence how susceptible the repro- 

 ductive system is to changed conditions, in the many 

 instances of animals rendered sterile by confinement ; 

 so that they will not unite, or if they unite do not 

 produce offspring, though the confinement may be far 

 from close ; and of plants rendered sterile by culti- 

 vation. But hardly any cases afford more striking 

 evidence how powerfully a change in the conditions of 

 life acts on the sexual elements, than those already 

 given, of plants which are completely self-sterile in 

 one country, and when brought to another, yield, even 



* Numerous cases together with the different organs of animals 



references are given in my ' Vari- are excited into different degrees 



ation under Domestication,' ch. of activity by differences of tempi- 



xxiii. 2nd edit. voL ii. p. 264. lature and food, and become to a 



With respect to animals, Mr. certain extent adapted to them. 



Biackenridge has well shown f 'Variation under Domestica- 



(' A Contribution to the Theory of tion,' ch. xii. 2nd edit. vol. i. 



Diathesis,' Edinburgh, 1869) that p. 466. 



2 o 2 



