298 The Botanical Gazette. [May, 
The physiology of tendrils. 
Our knowledge concerning the irritability of tendrils has 
been considerably enlarged by Dr. Carl Correns.! 
He finds that when the temperature surrounding tendrilsis 
either suddenly raised or suddenly lowered between suff- 
ciently separated extremes, a reaction, in all its phenomena 
like that released by a contact stimulus, is found to follow. 
The change, as such, affords the stimulus. 
When the entire tendril is exposed to the same tempera- 
ture conditions, it begins to roll in at the tip, continuing, if 
the temperature change be great enough, until several coils 
are formed. When the temperature is again brought to the 
normal, an unrolling of the tendril follows until it reaches 
again its original form. Or, if the new temperature limit is 
not so high as to produce a loss of sensitiveness, the tendril 
gradually accommodates itself to the new conditions when 
they are maintained, and uncoils, All the essential features 
of a typical reaction are to be observed. 
The minimum temperature difference necessary to cause 4 
perceptible reaction is, in case the experiments are conducted 
in the air, 10°C. ; when tendrils are immersed in water, 7-8°C. 
if the change of temperature is gradually made, no reaction 
is seen to follow. 
When the tendril is warmed locally, the reaction to the 
temperature change begins at the warmed place. 
Tendrils are found to bend in a plane fixed for each tendril 
by its physiologically bilateral structure; hence whether 
warmed from any one side or placed so that all sides af 
warmed alike, the curvature always takes place in a partic: 
lar predetermined plane. No tendrils observed were found 
to be Physiologically radial. ; 
The author decides that as far as he can discover, tendrils 
do not obey Weber's law concerning the relation of stimulus 
to reaction. 
As was noted in the April GAZETTE, MacDougal, in ae 
observed that a temperature elevation to 40°C. causes 4 ae 
ture of the whole tendril and local warming produces 2’? 
bending. He Says, ‘‘the results from these high and low tem 
Te 
*Bot. Zeit. 54: 1-20. 1896, 
