INTRODUCTION. 



n 



considered. Surely the true initiating cause resides 

 rather in the innate need or necessity of the organism 

 to form a particular structure under the stress of a 

 particular stimulus, this structure being brought into 

 being by the action of a regulative vital force. 



Goebel says that, in the case of the development of 

 double flowers, the " question is one of increase in the 

 quantity of the materials out of which the parts of the 

 flower are formed." But though the heaping up of 

 material may be the immediate stimulus, the formation 

 of a petal in place of a stamen would depend on the 

 presence of a regulative force in the plant. In the 

 same way the change of the direction of growth of a 

 root or stem under some special stimulus is not clue to 

 gravity as a regulative cause (i. e. the true primary 

 cause), but to this same vital force acting in direct 

 response to the needs of the plant. Here, again, 

 investigators show a tendency (so at least their phraseo- 

 logy suggests) to confuse the mechanism employed for 

 the gaining of a certain end with the true cause of the 

 modification. In brief, any morphological change, 

 whether normal or abnormal, is due to a re-adjustment 

 or re-adaptation on the part of the organism as the 

 result of the reception of some unusual stimulus. 

 Between the reception of the stimulus and the modi- 

 fication of structure there is an interval ; the action of 

 the stimulus is indirect ; the causal nexus between the 

 two is, so to speak, modified half way, and the inter- 

 vening factor is the instinct* of the plant, which takes 

 in hand the building of the new structure. 



The above paragraph is written merely in explana- 

 tion of the writer's attitude with regard to the etio- 

 logical aspect of the subject of this work. 



* Informed and gaiided by the past experience of the race. 



