THE MOVEMENTS AND HABITS OF PLANTS. 7 



crossing is concerned, unless their sexual elements are 

 thus affected. That every organism is acted on to a cer- 

 tain extent by a change in its environment will not, I pre- 

 sume, be disputed. It is hardly necessary to advance 

 evidence on this head ; we can perceive the difference be- 

 tween 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 gen- 

 erations under different climates or at different seasons 

 of the year transmit different constitutions to their seed- 

 lings. Under such circumstances, the chemical consti- 

 tution 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 compo- 

 sition. 



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. We have abundant 

 evidence how susceptible the reproductive system is to 

 changed conditions, in the many instances of animals ren- 

 dered 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 ren- 

 dered sterile by cultivation. 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 

 in the first generation, a fair supply of self-fertilized 

 seeds. 



