FREAKS OF PLANT LIFE. 



it to hold more firmly to its support, and withstand 

 greater shocks ; in addition to which the greater 

 thickness of the petiole would lessen its chance of 

 being forcibly unwound again from the twig it had 

 embraced. Several species of Tropceolum presented 

 somewhat similar phenomena in many respects. They 

 climb also by means of the curvature of the petioles 



Fig. 27. — Swollen petiole of Clematis vitalba. 

 of the leaves. The petioles are in some species 

 more sensitive than those of clematis. The slightest 

 rub caused them to bend in about three minutes 

 in one case, and in another species the petiole, after 

 a slight rub, became curved in six, eight, ten, and 

 in twenty minutes. It is not unusual to see the green 

 fruit capsules of the common nasturtium in gardens 

 bent over abruptly upon the stem, and even occa- 



