26 INTRODUCTION 



factors in the environment of the part affected, and hence must be included 

 in the category of external conditions. The influences emanating from 

 living aggregates may be of special character, and produce results possible 

 only to such living agencies. 



The entire vital mechanism involves a chain of interactions of an 

 extremely complex character. In fact, in order that all parts may influence 

 one another, and thus render possible a close correlation between the dif- 

 ferent members, it is absolutely essential for harmonious co-operation that 

 a corresponding readjustment of the entire mechanism shall be produced 

 in response to changes affecting the whole organism or any of its parts. 

 Without such continual readjustment, the continued existence and growth 

 of the organism would be impossible. Since all parts are' intimately 

 connected together to form a concrete whole, it follows that any automatic 

 or induced alteration in one organ must influence all the others, although 

 no directly perceptible result may be exhibited by them. In every 

 department of Physiology, cases may be found in which the different 

 component organs of a plant interact with one another in such a manner 

 that marked correlative changes are manifested by all of them, when any 

 one organ is compelled to undergo special modification. Thus, since root 

 and shoot supply particular forms of nutriment to each other, it follows 

 that when the functional activity of the root is depressed, the growth of the 

 stem must be correspondingly retarded. Moreover, since the consumption 

 determines the amount and direction of translocation, a cessation in the 

 consumption of a given substance must finally cause its absorption or 

 production to cease. A whole host of correlative phenomena of this kind 

 are exhibited by plants, and many of them have long been recognized '. 



Correlating influences are probably continually travelling from one part 

 to another, though they may only be made apparent by the character of the 

 changes induced by modifications of the primary arrangement or conditions. 

 The removal of particular members subtracts from the original aggregate 

 certain of the operating influences originally present, and hence alters the 

 character of the complex mechanism by which automatic correlation is 

 effected. The injury itself may, in addition, directly or indirectly induce 

 a creation of new relationships or modify the original power of reaction. 

 A variety of facts supports these conclusions : for example, the formation 

 of shoots from isolated roots, the development of dormant accessory 

 buds when the young spring shoots are removed, and the production of 



1 The term ' correlation ' is here used in the general sense in which it was employed by 

 De Candolle and C. Darwin, as including all physiological interactions, whether these find expression 

 as metabolic processes or formative changes. A further subdivision, according to the nature of the 

 causes at work, the character of the chain of intermediate processes, or the final result, is possible, 

 owing to the complicated nature of all correlative phenomena. See, for example, Herbst, Biol. 

 Centralbl., 1895, Bd. V, p. 724; Goebel, Flora, 1895, Erg.-bd., p. 195. 



