ARISTOLOCHIACEAE 



351 



states that three parts may be distinguished in them the base, the joint, and the hair 

 proper. The root of each hair is situated in a shallow depression of the perianth 

 and its basal cell is thick-walled. The joint, by means of which the hair bends, is 

 formed by one very thin-walled cell. The strength necessary for bearing the hair 

 is supplied by the hydrostatic pressure, which Corren showed to reach not less than 

 22 atmospheres. The hair itself consists of several thin-walled, plate-like cells. In 

 this case also the needful firmness is due to a high degree of turgidity (up to 

 15 atmospheres). The hair, which in its normal position is directed obliquely down- 

 wards against the pit, is depressed still further by a small insect forcing its way 

 in, and enabling it to pass on. The hair then springs back into its original position. 

 An insect is prevented from creeping out 

 again by a barrier (observed byHildebrand), 

 formed by a knob on the base of the 

 hair, which is directed upwards and im- 

 pinges against the wall of the perianth. 

 This barrier, however, is an imperfect one, 

 for the knob only touches the perianth at 

 one point, so that an oblique pressure can 



Fig. 356. Aristolochia Clemalttts, L. (after Sachs). A piece of stem {st), with a petiole {b), in the 

 axil of which a number of flowers are situated. i. Young still unfertilized flowers; 2, fertilized do., 



directed downwards (natural size). A and B. Flowers before and after pollination, in section (enlarged). 

 a, anthers ; f, inferior ovary ; k, trap ; kf, ovary in section ; / (in left-hand figure), limb of perianth, (in A) 

 a trapped insect ; n, stigma ; r, perianth tube. 



Correns (op. cit., p. 169 footnote) says that Sprengel's figure is better than the one from Sachs here 

 given, for it represents the hairs in the trap as^ minute prickles, and the weel-hairs as withered at the 

 beginning of the second stage. 



force the hair against the wall, the joint-cell undergoing torsion. The chief obstacle 

 to an insect's escape is to be found in the fact that the weel-hairs are considerably 

 longer than half the width of the perianth tube. They therefore usually cling 

 together in front of the barrier, so as to render escape impossible. 



