170 REVIEWS. 



eral lateral and on the terminal sub-petioles ; in a few hours 

 the latter were bent, but after 24 hours no effect was produced 

 on any of the lateral petioles. Again, a terminal sub-iietiole 

 placed in contact with a thin stick became sensibly curved in 

 45 minutes, and in 1 hour 10 minutes had moved through 

 ninety degrees, whereas a lateral petiole did not become sen- 

 sibly curved until 3 hours and 30 minutes had elapsed. In 

 this latter case, and in all other such cases, if the sticks be 

 taken away, the petioles continue to move during many hours 

 afterward ; so they do after a slight rubbing ; but ultimately, 

 if the flexure has not been very great or long-continued, they 

 become, after about a day's interval, straight again." — (p. 31.) 

 In numerous cases, notably in Solanum jasyninoidcs, the 

 petiole when clasped increases very greatly in thickness and 

 rigidity, undergoing a change in its woody structure by which 

 the fibro-vascular bundles, originally semi-lunar in cross-sec- 

 tion, develop into a closed ring, like that of an exogenous 

 stem. 



Lopho^permum scandens of the gardens climbs, like its 

 allies Maurandia and Rhodochiton, by clasping petioles ; but 

 in this plant, alone, the young internodes are also sensitive to 

 the touch. 



*' When a petiole clasps a stick, it draws the base of the 

 internode against it ; and then the internode itself bends 

 toward the stick, which is thus caught between the stem and 

 the petiole as by a pair of pincers. The int«node straight- 

 ens itself again, excepting the part in contact with the stick. 

 Young internodes alone are sensitive, and these are sensitive 

 on all sides along their whole length. I made fifteen trials 

 by lightly rubbing two or three times with a thin twig several 

 internodes ; and in about 2 hours, but in one case in 3 hours, 

 all became bent ; they became straight again in about 4 hours, 

 sid)sequently. An internode, which was rubbed as much as 

 six or seven times with a twig, became just perceptibly curved 

 in 1 hour 15 minutes, and subsequently in 3 hours the curva- 

 ture increased much ; the internode became straight again in 

 the course of the night. I rubbed some internodes one day on 

 one side, and the next day on the opposite side or at right 



