GENERAL PROPERTIES OF GROWING PARTS OF PLANTS. 705 



repeated bendings constantly in opposite directions leave progressively smaller curv- 

 atures^; (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 concave and convex sides of a bent interiiode. Here 

 again, as in paragraph b, 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 lefi to itself, were measured by means of a carefully applied strip of card divided 

 into millimetres. In order to get a great difference between the concave and convex 

 sides, very thick internodes were selected, and their thickness measm-ed in the 



middle. 



Radius of t .1 • 



T M f Radius of ^ Contraction Lengthening 



,T. Length of curvature ^ , . , 



Name. . *= curvature i, 1 r. of the of the 



internode. , , when lelt 



when bent. •. ir concave side, convex side. 



Silphiiim pe7foliatu7n 

 13-2 mm. thick. 



Before bending . . 185 mm. 



Bent .... 14 cm. 26 cm. I mm, 2 mm. 



Bent in opposite direct. . 14 30 i i'5 



Straightened . . .185 



L igularia inacroph} 'lla 

 7-5 nnii. thick. 



Before bending . .199 



Bent .... 



Bent again . 



Bent in opposite direct. . 



These observations show, as was to be expected, that the permanent curvature 

 of an internode is connected with a permanent contraction of the concave and 

 lengthening of the convex side. 



{d) The region of greatest flexibility, and at the same time of least elasticity in 

 growing shoots, appears to coincide with the spot where the maximum rapidity of 

 growth exists {vide infra, Sect. 17) or is just past; more exact determinations are 

 however wanting on this point. If a number of rapidly growing shoots are cut off 

 at a point where there is no longer any growth in length, and if this place is taken 

 in one hand and the terminal bud in the other hand (after the removal perhaps of the 

 older leaves), and the shoot is then bent tolerably vigorously by a pull at the bud, it 

 may be seen, with the aid of a card on which a number of concentric circles have 

 been drawn, that the strongest curvature (with the smallest radius of curvature) takes 

 place at a point at a great distance, often as much as 10 or 20 cm., from the bud, 



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

 z z 



