150 Controversial Questions. 



variability of vegetative organs and the equally remark- 

 able uniformity of organs connected with reproduction; 

 and further the dissimilarity between seeds on one and 

 the same plant. 



Vegetative organs are as a rule much more variable 

 than those which are concerned with sexual processes. 

 The characters of flowers exhibit very slight variability : 

 and the more they are adapted to the visits of insects the 

 less variable are they. The number of petals and stamens 

 is remarkably constant so long as the number is small; 

 but when their number becomes so great that a few more 

 or less would exert no perceptible influence on the shape 

 of the flower, it ceases to be constant. The symmetry 

 of the flower is hardly subject to variation at all. The 

 more exactly a flower is adapted to the visits of single 

 genera or species of insects the more serious would any 

 deviation from the normal form be ; and we do as a mat- 

 ter of fact find that in such cases deviations are exceed- 

 ingly minute and rare. On the other hand when we con- 

 sider the vegetative life of a plant we see that it is of the 

 highest importance that the plant should be able to make 

 the most of the amount of light, moisture, inorganic 

 food, and space at its disposal, that is, to be in a posi- 

 tion to develop luxuriantly in favorable circumstances 

 and economically in unfavorable ones. 



There is a whole series of plants which are remark- 

 able for an extraordinary plasticity of this kind. It is 

 often assumed that the general conditions affecting the 

 growth of a plant on such a small area as a garden bed 

 are in themselves uniform or at any rate that they can 

 be easily made so. But my experience, which is derived 

 from such experiments extending over more than ten 

 years, has convinced me that the difliculties in the way of 



