co8 LECTURE XXX. 



capability ot the organ to react towards gravitation — is eo ipso modified; and 

 it may be shown in other cases how by such interferences even the reaction 

 to the action of light of the organ which is being modified becomes changed. 



From the small number of examples by which I have sought to illustrate the 

 conception of correlation of growth, it is not to be concluded that we are here 

 concerned only with incidental and isolated phenomena : on the contrary, we 

 have every reason to believe that similar relations between the growth of any one 

 organ and that of all the others of a plant, however diflScult to detect, are very 

 general. In animals, and. especially the more highly organised species, a mutual 

 correlation, in consequence of the sharply marked individuality, not only exists 

 between all the organs (which, it is true, are all nourished by the same blood), but is 

 also more easily intelligible than in the case of plants ; for from daily but superficial 

 experience, the very common opinion has been formed that in plants every organ 

 is formed and grows quite independently of the others. The possibility of raising 

 new entire plants from cut-ofF pieces of leaves, shoot-axes, or roots, by the regene- 

 ration of the missing organs, easily leads to the belief that no intimate mutual 

 relation of the vegetable organs at all exists. But a deeper insight into the whole 

 nature of vegetation leads to the opposite conclusion. In the plant also, it is true that 

 every growing organ derives its constructive materials from the common store of 

 nutriment which is collected and distributed in the tissues by the assimilation of the 

 leaves, or has been deposited in quantities in the reservoirs of reserve-materials from 

 a previous period of vegetation; and it is obvious that when numerous different 

 organs are simultaneously drawing their materials for growth from the common store, 

 one may take what the other needs, and it may happen, as for example the experi- 

 ment of Prunus padus cited above teaches, that through the growth of a shoot the 

 simultaneous growth of its lateral buds may be prevented. Above all, from this point 

 of view, equivalent organs must be regarded as competitors at the common store 

 of unsorted nutriment : the growth of a shoot will re-act especially on that of other 

 shoots, the growth of a root chiefly on that of other roots; since it requires no 

 proof that the mixtures of materials which the shoots draw from the common store 

 of nutriment of the plant differ in nature from those which afford the constructive 

 materials of the roots. In the same way experience teaches that in the nutritive 

 substances produced by assimilation and altered further by metabolism, peculiar 

 mixtures of materials become differentiated from which the sexual organs and (in 

 the Phanerogams) the flowers arise. If the first young flower-buds are removed 

 from a plant, the usual result is that other much younger flower-buds, which would 

 probably not have developed at all, begin to grow so much the more vigorously ; or 

 that flower-buds, the rudiments of which are not yet formed, arise at places where 

 they would not have arisen at all without the interference — a fact upon which the 

 old knowledge of fruit-culture in part depends. If the flowers, foliage, shoots, and 

 roots were constructed from the same mixtures of substances, it would not be 

 obvious why the removal of young flower-buds should not also call forth an 

 invigorated growth of leaves and roots. The latter indeed occurs under certain 

 circumstances, but only in consequence of further interdependencies which we 

 cannot here follow further. Here also we are not further interested in the question 

 how we are to imagine the production chemically, as it were, of these various 



