2 o6 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



drawn between our subject and physiology, but we shall always endeavour 

 to consider our facts from the organographical point of view, as is done 

 by Hofmeister in his classical 'Allgemeine Morphologic,' a work which 

 expressly adopts an experimental treatment of morphological questions, 

 and thereby stands out in striking contrast with the idealistic morphology 

 of its day. 



There are two branches of experimental organography which we have 

 to consider : 



I. The reciprocal influence of organs upon one another ; this is 

 termed correlation ; 



II. The influence of external factors which, with Herbst 1 , we may 

 call formative stimuli. In the Fourth Section dealing with malformations 

 examples of such formative stimuli have been cited. 



I. CORRELATION 2 . 



The facts mentioned in the chapter upon regeneration 3 have shown 

 that the organs of many plant-bodies can under favourable conditions 

 continue their life after being separated from the parent plant. Thus in 

 the operation of budding we remove buds, in the case of grafting we 

 take off whole shoots from the tissues with which they were previously 

 connected, and unite them with others ; leaves also and roots may be 

 removed from a plant and placed upon another, either of the same or of 

 a different species, and they grow on and continue their life-phenomena. 



We might be led to conclude from these facts that the organs possess 

 a far-reaching independence one of the other. Careful research however 

 shows that this is not the case and demonstrates the existence of a recipro- 

 city between parts of the plant-body ; the size and construction of one 

 organ is frequently determined by those of another 4 . These reciprocal 



1 Herbst, Bedeutung der Reizphysiologie fur die Ontogenese, in Biol. Centralbl. ; 1895, p. 721. 

 I specially direct attention to this excellent treatise. 



2 See Goebel, Beitrage zur Morphol. und Physiol. des Blattes, in Botan. Zeitung, 1880, p. 753; 

 Id. liber die gegenseitigen Beziehungen der Pflanzenorgane. Berlin, 1884 this paper has been 

 much used in preparing the account given here ; Id. Zur Geschichte unserer Kenntnis der Korrelations- 

 erscheinungen I, in Flora, 1893, p. 38, and II in Flora, Erganzungsband, 1895, p. 195, where the 

 older literature is cited. 



z See p. 43. 



1 One might also say, through its relations to the system of organs to which it belongs, a system 

 which forms to a certain extent an interdependent whole and endeavours if it be injured to reconstruct 

 itself again as far as possible. Of the existence of a 'system' we are assured from the facts of 

 correlation, and it appears to me to be of subordinate importance whether, with Herbst, we see in 

 injuries such as the severance of the top of a conifer the ' alteration of the system ' or a direct 

 influencing of the organ. The influence of the separation of the top is that the position of the 

 uppermost lateral shoots in the ' system ' becomes different and in conformity therewith their growth 

 and relationships of configuration are changed. 



