246 Influence of Environment on Plants 



Good manuring is in the highest degree favourable to vegetative 

 growth, but is in no way equally favourable to the formation of 

 flowers. The constantly repeated expression, good or favourable 

 nourishment, is not only vague but misleading, because circum- 

 stances favourable to growth differ from those which promote repro- 

 duction ; for the production of every form there are certain favourable 

 conditions of nourishment, which may be defined for each species. 

 Experience shows that, within definite and often very wide limits, it 

 does not depend upon the absolute amount of the various food sub- 

 stances, but upon their respective degrees of concentration. As we 

 have already stated, the production of flowers follows a relative 

 increase in the amount of carbohydrates formed in the presence of 

 light, as compared with the inorganic salts on which the formation of 

 albuminous substances depends^ The various modifications of flowers 

 are due to the fact that a relatively too strong solution of salts is 

 supplied to the rudiments of these organs. As a general rule every 

 plant form depends upon a certain relation between the different 

 chemical substances in the cells and is modified by an alteration of 

 that relation. 



During long cultivation under conditions which vary in very 

 different degrees, such as moisture, the amount of salts, light in- 

 tensity, temperature, oxygen, it is possible that sudden and special 

 disturbances in the relations of the cell substances have a directive 

 influence on the inner organisation of the sexual cells, so that not 

 only inconstant but also constant varieties will be formed. 



Definite proof in support of this view has not yet been furnished, 

 and we must admit that the question as to the cause of heredity 

 remains, fundamentally, as far from solution as it was in Darwin's 

 time. As the result of the work of many investigators, particularly 

 de Vries, the problem is constantly becoming clearer and more 

 definite. Tlie penetration into this most difficult and therefore 

 most interesting problem of life and the creation by experiment 

 of new races or elementary species are no longer beyond the region 

 of possibility. 



1 Klebs, Kiinttliche Metamorphose n, p. 117, 



