CHAPTER XIV 



EFFECT OF MOLAR AGENTS UPON GROWTH 



It is proposed in this chapter to consider, first, the effect of 

 contact, rough movements, deformations, and associated molar 

 agents upon the rate of growth, and, secondly, the effect of 

 such agents upon the direction of growth. 



§ 1. Effect of Molar Agents upoisr the Rate of 

 Growth 



We have already (Chapter IV) seen that profound changes 

 in metabolism and the motion of protoplasm are induced by 

 various sorts of contact. We shall here consider how those 

 changes result in modifications of growth. 



1. Contact. — In the case of organs which normally grow 

 upon a solid substratum the growth may take place more 

 rapidly after coming in contact than before. Thus Loeb ('91, 

 p. 29) says of the stolons of the hydroid Aglaophenia pluma, 

 that when they reach a solid surface they begin to grow 

 more rapidly than stolons which develop free in the water. 

 Evidently the stimulus of contact excites to extraordinary 

 growth. 



2. Rough Movements. — Experiments with this agent have 

 been almost confined to bacteria, and have been made by shak- 

 ing. The first experimenter in this direction was Hoevath 

 ('78), whose method of work is worth giving in some detail. 



Glass tubes about 20 cm. long and 2 cm. -wide were half filled by a nutri- 

 tive fluid, inoculated with an infusion full of various bacteria, and sealed. 

 The tubes were then fixed on a board which was made to swing horizontally 

 to and fro by means of a motor through an arc of about 25 cm. length at 

 the rate of 100 to 110 times per minute. At the end of each excursion the 

 board received, by means of a special device, an extra blow. The resulting 

 agitation was like that made in shaking a test-tube: 



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