GENERAL PROPERTIED' OF GROWING PARTS OF PLANTS. 



707 



nent curvature is produced in this region, but it is in this case convex to the side 

 from which the blows came. 



In all the cases w^hich I have described the position of the permanent curvature 

 is the same as that of the strongest curvature, even if acquired only momentarily 

 by the shoot. The appearance is precisely the same as if the shoot were taken in 

 the hand and then strongly bent once, or as if it were repeatedly bent backwards 

 and forwards, but more strongly in one direction. Mere concussions which produce 

 no strong flexion of the shoot cause no permanent curvature ; if shoots are 

 enclosed in glass tubes and violent impulses repeatedly imparted to them by jerking 

 the tubes upwards or swinging them from side to side no change is visible when 

 the shoots are removed from the tube. 



If the part of a shoot susceptible of curvature is marked with ink in equidistant 

 divisions, and then made to oscillate by blows below this part, the convex side of 

 the permanent curvature is then found to have become longer, the concave side 

 shorter, precisely in accordance with the phenomena described in Sects, d and c \ 

 For the measurements in the following table as thick shoots as possible were used, 

 since they give considerable differences in length between the convex and concave 

 sides even when the curvature is slight. The measurements w^ere made with strips 

 of card graduated in millimetres, and which I applied closely to the concave and 

 convex sides. 



Approximate 

 radius of 

 curvature. 



18 cm. 



Name. 



( )ri£;inal 

 length. 



Silphiiiiu p:rfolialnm 



do. do. . 



Machya coniata . 

 do. do. . 



Pol) -gon um L ^agoj]} 'rum 

 Hdiaiithus tuberosiis 

 Valeriana cxaltaia 

 do. do. . 



Vitis 7'iuifera 



If) 2 mm. 

 I 20 



B7-5 

 104 



98 

 150 

 1 10 

 149 



7 

 24 



32 



6-10 



The permanent curvature which remains after violent oscillations of a shoot, or 

 the Ciu'vaiure of Concussion, is the result of a lengthening of the convex and a 

 simultaneous contraction of the concave side. A proof is thus afforded that the 

 whole phenomenon is dependent on the very imperfect elasticity and the great 

 flexibility of the region that is capable of flexion^. A shoot bent in this way shows 

 the same changes as one that is simply bent between the hands. This result 



^ According to Hofmeister all the sides of the shoot become longer. He calculated the length 

 of the curve which he took for an arc of a circle; andPrillieux measured only the concave side, which 

 he found to be always shorter ; the contraction of the whole shoot, i. e. of its neutral axis, cannot 

 however be inferred from that of the concave side. The thickening which, according to Hofmeister, 

 should take place, if the shoot becomes longer on all sides, I consider cannot be demonstrated, in 

 consequence of the extremely small change in diameter which takes place in such cases. 



^ Compare the different description given by Hofmeister in his paper On the Bending of the 

 Succulent Parts of Plants, in the Berichte der kon. sachs, Ges. der Wiss., 1S59. 



z z 2 



