EFFECT OF TEMPERATURE 



141 



response, I find in the case of the plant Biophytum that the 

 effect of too great cold, or of long-continued exposure to low 

 temperature, is the abolition of its lateral response. But 

 when the temperature is, relatively speaking, only slightly 

 lowered, induced sluggishness is shown in a very interesting 

 manner. Whereas, at the normal temperature, say 23 C, 

 the response of the leaflet of Biophytum takes place imme- 

 diately, after moderate cooling, on the contrary, the latent 



CL 



ct i 



Ivy Holly Eucharis 



Fig. 76. After-effect of Cold on Ivy, Holly, and Eucharis 



(a) Normal response ; (l>) response after subjection to freezing temperature 

 for twenty-four hours. 



period is increased, and response does not begin to take place 

 until from one to two seconds after the application of stimulus. 

 Lowering of temperature also abolishes the autonomous 

 response of Desmodium. 



(c) Diminution of longitudinal response. — With regard to 

 longitudinal response, I have been able to demonstrate the 

 effect of cold, by taking a specimen of the coronal filament 

 of Passiflora. The specimen was kept for fifteen minutes 

 in ice, after which electrical stimulus was applied with no im- 

 mediate contractile effect. Control specimens, on the other 

 hand, exhibited considerable contraction. These contractions 

 were measured in both cases by means of a micrometer. The 

 specimens taken for experiment were all 21 mm. in length. 

 The average contraction of the control specimens was 

 1*5 mm. The cooled specimen, as said before, exhibited 

 no immediate response. But on continuing stimulation for 

 two minutes, contraction began to take place slowly, reaching 

 a maximum of only '5 mm. It must be borne in mind 



