MUTUAL COMPETITION OF ORGANS. 509 



organ-forming mixtures of substances. Considerations on this point * are found in 

 my treatises 'On the Substance and Form of the Organs of Plants^ and later, when 

 we are concerned with reproduction, I shall probably find opportunity of taking up 

 the subject again. Here my intention is to mention only one of the most essential 

 and important factors which co-operate in the correlation of growth, but by no 

 means to assert that still other causes do not interfere and affect the matter. 

 Above all there is one point to be insisted upon — that the various organs growing 

 from the common nutritive material of the plant, and as competitors for that 

 material, stand opposed to one another in a certain sense as enemies; though, 

 on the other hand, it is to be noticed that the various organs, especially shoots and 

 roots, afford support to one another by their functions, and are so far indispensable 

 to one another. This latter is the case, however, as a rule, only when they are 

 fully grown and completely developed for their specific function : a mature, fully 

 grown foliage-leaf promotes the production of new foliage-shoots, because by means 

 of its assimilation it affords new material for growth, and so forth. Considerations 

 of this kind, however, would carry us into matters of which I have already treated in 

 detail in the theory of nutrition. 



Again, it cannot be expected that all correlations of growth are so easy to 

 demonstrate by experimental interference on the part of the observer, as in the 

 cases considered above : on the contrary, causes may exist in the plant which lead 

 the result of such experiments into paths quite different from those desired. How- 

 ever, even without experimental interference we may, supported by what I have so 

 far stated, obtain a deeper insight into very extensive correlations of the whole 

 organisation of a plant. As one example I might especially quote the relations, 

 repeatedly indicated in previous lectures, which exist between the properties of the 

 chlorophyll and the whole external and internal organisation ; this is of such a kind 

 that one may regard, without exaggeration, the whole relations of form in the 

 vegetable kingdom, and particularly the very different aspect of plants in comparison 

 with that of animals as depending on the properties and activities of chlorophyll. In 

 this of course we enter upon a province which extends far beyond that of the 

 correlations of growth shown above, but still, since the whole organisation of a 

 plant is the result of its growth, we may nevertheless take into our present sphere of 

 thought what follows. 



It is my intention to show somewhat more in detail, that, as a matter of fact, the 

 most essential relations of organisation of the plant are causally determined by the 

 properties of chlorophyll. 



We may start from the fact that the cells which contain chlorophyll are the only 

 assimilatory organs of the plant, and that they alone are able to produce, from carbon 

 dioxide and water, organic and organisable substance suitable for the growth of new 

 organs, and that for this purpose they require those materials which can only be absorbed 

 from the soil by means of the roots, the so-called ash-constituents, with which a 

 nitrogenous compound, nitric acid, is associated for the purpose of forming proteids. 



' Sach's ' Staff und Form der Pflanzenorgane ' (Arb. des bot. Inst, in Wzbg. B. II, H. 3, 1880, 

 p. 452, and H. 4, 1883, p. 689). 



