SUBJECTS TO BE DISCUSSED 3 



In spite of much theorising, no clear idea has yet been 

 reached concerning the ultimate mechanism of growth in 

 the individual cell. It is not possible to go beyond the 

 statement that the growth of the cell depends upon its 

 turgidity, the degree of which, and also the rate of growth, 

 are regulated by the cell-protoplasm . Fundamentally, there- 

 fore, the mechanism of growth is the same as that of other 

 plant-movements. 



For the purpose of observing the rate of growth in length, 

 auxanometers magnifying about 20 times have been in 

 general use. Even with this magnification it takes several 

 hours to measure the rate of growth and the change induced 

 in it by any particular stimulus. The external conditions 

 cannot, however, be maintained constant for such a pro- 

 tracted period, and the observed result is vitiated by the 

 effect of change in these factors. 



The possibility of accurate investigation, therefore, lies 

 in reducing the period of the experiment to a few minutes 

 during which the external conditions can be maintained 

 constant, thus making possible the accurate determination 

 of the variation of rate of growth induced by any one mode 

 of stimulation. This necessitates the devising of a method 

 of high magnification for the record of growth. 



Among the subjects discussed in the present volume are : 



1. Absolute determination of the rate of growth by 

 several sensitive and exact methods. 



2. Quantitative determination of changes induced in 

 growth under variation of external conditions. 



3. The modifying influence of tonic condition on response 

 to external stimulation. 



4. The effect of radiant energy through a wide range 

 of the ethereal spectrum. 



5. The effects of direct and indirect stimulation on 

 growth. 



6. Tropic curvature under unilateral stimulation. 



7. The modification of tropic curvature by transverse 

 conduction of excitation. 



