Chap. UI. OF THE EADIOLE OP THE PEA. 



159 



trial was made in the same manner with 15 radicles ; 

 but from circumstances, not worth explaining, they 

 were only once and briefly examined after the short 



Fig. 66. 



A. B. 



Pisutn sativum : deflection produced within 24 hours in the growth of 

 vertically dependent radicles, by little squares of card afiixed with 

 shellac to one side of apex : A, bent at right angles ; B, hooked. 



interval of 5 h. 30 m. ; and we merely record in our 

 notes " almost all bent slightly from the perpendicular, 

 and away from the squares ; the deflection amounting 

 in one or two instances to nearly a rectangle." These 

 two sets of cases, especially the first one, prove that 

 the apex of the radicle is sensitive to slight contact 

 and that the upper part bends from the touching 

 object. Nevertheless, on June 1st and 4th, 8 other 

 radicles were tried in the same manner at a tempera- 

 ture of 58°-60° F., and after 24 h. only 1 was decidedly 

 bent from the card, 4 slightly, 2 doubtfully, and 1 not 

 in the least. The amount of curvature was unaccount- 

 ably small ; but all the radicles which were at all bent, 

 were bent away from the cards. 



We now tried the effects of widely different tempera- 

 tures on the sensitiveness of these radicles with squares 



