"general properties of growing parts of plants. 787 



shorter, precisely in accordance with the phenomena described in paragraphs ^ 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 were made with strips 

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

 convex sides. 



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

 the Cur'vature of Concuss ion^ is the result of a lengthening of the convex and a 

 simultaneous shortening 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 

 would not be at all altered were it found, in harmony with what was said in para- 

 graph b, that the concave side was also sometimes slightly lengthened, since it is 

 stretched by the recoil of the oscillations; and this elongation is not always entirely 

 neutralised. Prillieux has compared this curvature to that of a lead-wire fixed to 

 an elastic support, when the support was struck ; he was unable however to see 

 the reason why the older and younger parts of the shoot did not exhibit the phe- 

 nomenon. In the older parts this depends on their more perfect elasticity, in the 

 younger on their smaller flexibility, and on the circumstance that they are not 

 strongly bent, but are only thrown backwards and forwards by the oscillations of 

 the lower and more flexible parts. 



The subsequent neutralisation of the curvature by growth must depend first of 

 all on the increase of turgidity in the concave and its diminution in the convex 

 side, and on the growth being consequently promoted in the former. This may 

 be assisted also by the secondary effect of elasticity, in consequence of which the 

 stretched epidermis of the convex side shortens, while the compressed tissues of 

 the concave side expand. 



Sect, i 4. — Causes of the condition of Tension in Plants. The elasticity 

 of the organised parts of plants results in tension chiefly from the operation of three 

 causes; viz. (i) the turgidity, in other words the hydrostatic pressure of the conter* 

 of the cell on the cell-wall; (2) the swelling and contraction of the cell-wal^' 



aiated the length 

 * According to Hofmeister all the sides of the shoot become longer. ^f^Q QoxiCz.\e side, which 

 of the curve which he took for an arc of a circle ; and Prillieux measured o^^ ^^.^ neutral axis, cannot 

 he found to be always shorter ; the contraction of the whole shooj^j^/j^ according to Hofmeister, 

 however be inferred from that of the concave side. The thicke-^^^.^^^. ^^^^^ ^^ demonstrated, in 

 should take place, if the shoot becomes longer on all sidj^^ ^^^^^ .^^ i^ ^^^h cases, 

 consequence of the extremely small change in diamete-^ .^ ^^ 0„ the Bending of the 



^ Compare the different description given bv^"""''" '^ tRco 



Succulent Parts of Plants, in the Berichte der i^"- ^achs. Ges. der VYiss., 1059- 



3 E 2 



