Porometer and a Note on Stomatal Behaviour during Wilting. 55 
at least one plant, Eucharis amazonica , it was possible in a porometer 
experiment with a normal attached leaf, that some of the air drawn from the 
leaf entered it through the petiole and not through the stomata, since, when 
all the stomata outside the leaf-chamber were blocked, a current of air could 
still be drawn through the leaf unless the petiole was severed and blocked, 
e. g. by immersing in water. 
It was thought possible therefore that when a leaf was detached from 
the plant and the petiole exposed, the air-stream might find the path 
through the petiole of less resistance than formerly. This would result 
in an increase in the speed of the air-current through the leaf, followed 
by a decrease when the stomata closed. 
If this were the case, it is to be expected that the temporary ‘ opening ’ 
would reach a maximum almost immediately after detaching the leaf. The 
results show that some minutes elapsed in every case before the maximum 
was reached, which also confirms the observations of Darwin and Pertz. 
This explanation of the phenomenon applies only to the results obtained 
by the porometer method, but Darwin’s experiments with the horn hygro- 
scope and temperature methods (4 and 5) showed clearly that an increase 
in transpiration occurred when the leaf was detached ; this he adduced as 
further evidence for the view that the stomatal apertures had increased. 
Dixon (8) has, however, suggested that the result of detaching a leaf is 
to reduce the tension in the water columns in the tracheae and thereby 
permit of more active evaporation from the mesophyll cells. 
Experimental tests of these possible explanations were undertaken, 
using chiefly Phaseolus vulgaris , Eupatorium adenophorum , and Maranta 
coccinea , var. Jioribunda. 
To prevent any flow of air through the petiole after severing it, the cut 
end was blocked by various means. Vaseline was found to be unsatisfactory 
owing to the difficulty of attaching it to the wet surface. Immersion in 
mercury, and coating the end with a wax mixture, stiff gelatine and stiff 
glue, were among the methods used to close the cut end of the petiole. The 
results showed that blocking the petiole by these means did not prevent the 
usual temporary opening, even though, in the case of the experiments with 
gelatine, the petiole was cut beneath the surface of liquid gelatine, and the 
cut end was therefore never exposed to the air. The phenomenon cannot 
therefore be attributed to the leakage of air through the petiole. 
If, however, the petiole is cut below the surface of water, and kept 
supplied with water, the temporary opening does not occur. Instead there 
is either a slight tendency to closure, or else the stomata behave quite 
similarly to those of the control leaf still attached to the plant. Under these 
conditions the leaf does not visibly wilt in the course of several hours, 
or at most is only slightly less turgid than the leaves attached to the plant. 
This result disposes of the possibility of shock being responsible for the 
