GENERAL PROPERTIES OF GROWING PARTS OF PLANTS. 



785 



These examples, selected from a long series of observations, show: — (i) that 

 growing internodes are very flexible, (2) that after bending they do not altogether 

 recover their straightness, or that the elasticity of curvature is imperfect; (3) that 

 repeated bendings constantly in opposite directions leave progressively smaller curva- 

 tures^; (4) that one vigorous bending, and to a still greater extent repeated ones 

 in opposite directions, leave the internode flaccid, or deprive it of its rigidity (of 

 which no special account is taken in the table) ; and (5) in the case of the three first 

 examples, that an internode bent first in one and then in another direction lengthens 

 slightly, while in the case of the two last there was no lengthening, but in one even 

 a perceptible contraction. 



(c) Change of length of the conca've and con-vex sides of a bent internode. Here 

 again, as in paragraph ^, the bending was done by the hands, and measured by the 

 radius of curvature on a card on which concentric circles were drawn. The original 

 length, as well as those of the sides which remain concave and convex after the object 

 is left to itself, were measured by means of a carefully applied strip of card divided 

 into millimetres. In order to get a great diff'erence between the concave and convex 

 sides, very thick internodes were selected, and their thickness measured in the 

 middle. 



Name. 



Silphium perfoliatum 

 13*2 mm. thick. 



Before bending 



Bent . . . . 



Bent in opposite direct. . 



Straightened . 

 Ligularia macrophylla 

 7*5 mm. thick. 



Before bending 



Bent . . . . 



Bent again 



Bent in opposite direct. . 



length of 

 internode. 



185 mm. 



Radius of 

 curvature 

 when bent. 



Radius of 

 curvature 

 when left 

 to itselt 



Contraction 



of the 



concave side. 



Lengthening 



of the 

 convex side. 



185 



199 



17 



13 

 30 



3*5 



3*5 



•5 



4 



4*5 



1*5 



* The curvature is less the greater the radius of curvature. 

 3 E 



