424 CHAP. XXXVII. GENERAL REVIEW 



short time ; but intense stimulation caused by a wound 

 gives rise to a greater and more persistent retardation of 



growth (p. 89). 



Effect of photic stimulation. — The normal effect of light 

 is an incipient contraction or retardation of growth. The 

 after-effect of brief and moderate stimulation by light is 

 an acceleration of growth above the normal rate. The 

 effectiveness of the different rays of the visible spectrum in 

 retarding growth undergoes a decline from the blue to the 

 yellow-red (p. 78). 



Radio-thermal stimulation. — The effectiveness of the 

 infra-red rays in retarding growth undergoes sudden aug- 

 mentation when the rays of heat are reached (p. 79). 



Response to wireless stimulation. — The effect is found to 

 be essentially similar to that under the action of visible 

 light. Under strong intensity of stimulation the response 

 is a retardation of growth. Under feeble intensity of 

 electric waves the response is an acceleration of growth, 

 which is also the characteristic effect of feeble light (p. 189). 



Effect of high-frequency alternating field of electric force. — 

 The effect of this is analogous to that of wireless electric 

 waves. The response is modified, as in the case of visible 

 light, by the intensity of stimulation and by the tonic 

 condition of the tissue ; feeble stimulation induces an 

 acceleration, while strong stimulation causes a retardation, 

 of growth. These facts offer a satisfactory explanation of 

 the anomalous results obtained by different observers on 

 the effect of high-tension alternating current on growth. 



Effect of Tonic Condition on Response 



The sign of response, negative or positive, is dependent 

 on the tonic condition. Mimosa in a subtonic condition 

 responds to stimulation by an abnormal positive or erectile 

 movement instead of by the normal negative fall of the leaf. 

 Under continuous stimulation the tonicity is raised to a 

 condition of par, the abnormal positive response being now 

 replaced by the normal negative. The effect of stimulation 



