MOVEMENTS OF IRRITATION. 



497 



round in space, and are more likely to encounter suitable supports, 

 to which they can attach themselves. 



If it is desired to investigate carefully the irritability of 

 tendrils, Sicyos angulatus is specially to be recommended as 

 research material, and I have carried out many experiments with 

 ifc. When young, the separate branches of the tendrils of this 

 plant are spirally coiled. When however they have extended, and 

 while still actively growing, they become exceedingly sensitive- 

 At a low temperature naturally the irritability is less than in very 



FIG. 166. Portion of a shoot of Sicyos angulatus with a tendril. 



warm weather. If, on a warm day, we carefully draw an extended 

 tendril branch between the fingers, it at once curves considerably 

 and the movement exhibited is so rapid that we can follow it 

 directly with the eye. Fig. 166 shows part of a shoot of Sicyos 

 angulatus bearing a tendril. One branch a is not stimulated, and 

 so is still extended in a straight line. The branch 6 having been 

 slightly stimulated by means of a thin wooden rod has per- 

 formed an inconsiderable curvature, while the branch c having 

 been strongly stimulated has performed a vigorous curvature. 

 To the branch d we shall return later. If a tendril of Sicyos 



P.P. K K 



