tkansmttted effect of light ^(jD 



perception and heliotropic excitation are two distinct pheno- 

 mena, which depend on different properties of the proto- 

 plasm and which are independent of each other . . . 

 We may, therefore, conclude from this experiment that these 

 two types of excitation are fundamentally distinct pro- 

 cesses, for it is only after indirect or transmitted and not 

 after direct excitation that a reaction occurs in the c.ise 

 of the seedlings of the Paniceae ".* 



The noteworthy deductions on the above facts are : — 



(1) That the motile organ in Setaria is totally devoid 



of perception, since direct action of light induces 

 no effect. 



(2) That perception and heliotropic excitation are two 



distinct phenomena, which depend on different 

 properties of the protoplasm, and which are 

 independent of each other. 



Though the conclusions thus arrived at appear to fol- 

 low from the facts that have been observed, yet it is 

 difficult to accept the inference, that a responding organ 

 should be totally devoid of the power of perception, and 

 that excitation and perception are to be regarded as de- 

 pt'ndent on different properties of protoplasm. It there- 

 fore appeared necessary to re-investigate the subject of the 

 perceptive power of the cotyledon, and the responding 

 characteristics of the hypocotyl. 



The criterion employed for test of perception is the 

 movement induced in response to stimulus. The respon- 

 sive mechaiiicnl movement is rendered possible only by the 

 contractility of the organ, and mechanical and anatomical 

 facilities offered by it for unhampered movement. The 



• Joat -lbid-\>. 468. 



