92 MR. DAKWIK OK CLlMBI>'a PLANTS, 



the Vitaceae, Sapindacege, and Paasifloraceae, are modified flower- 

 peduncles. This is likewise the case, according to De CandoUe (as 

 quoted by Mohl), with the tendrils of Brunnichia^ one of the 

 Polygonacese. In two or three species of Modecca^ one of the 

 Papayacea^, the tendrils, as I hear from Prof. Oliver, occasionally 

 bear flowers and fruit ; so that at least they are axial in their nature. 

 Spiral contraction of Tendrils. — This movement, which shortens 

 the tendrils and renders them elastic, commences in half a day or 

 in a day or two after their extremities have caught some object- 

 There is no such movement in any leaf-climber, with the exception 

 of an occasional trace of it in the petioles oi Trop^olum tricolorwn. 

 On the other hand, it occurs with all tendrils after they have seized 

 some object, with the few following exceptions,^ — namely Corydalis 

 claviculata, but then this plant might still be called a leaf-climber; 

 Hignonia unguis and its close allies, and the CardiospermuM ; though 

 these tendrils are so short that the contraction could hardlv take 

 place, and would be quite superfluous ; and Smila.v asj^era^ the 

 tendrils of which, though rather short, offer a more marked excep- 



4 



tion. In the Dicentra^ whilst young, the tendrils are short and do 

 not contract spirally, but only become slightly flexuous ; the longer 

 tendrils, however, borne by older plants contract spirally. I have 

 seen no other exceptions to the rule that all tendrils, after clasp- 

 ing by their extremities a support, contract spirally. When, how- 

 ever, the tendril of any plant of which the stem happens to be 

 immoveably fixed, catches some fixed object,, it does not contract, 

 simply because it cannot ; this, however, rarely occurs. In the 

 common Pea only the lateral branches, and not the central stem 

 of the tendril, contract ; and with most plants, such as the 

 Vine, Passiflora, Bryony, the basal portion never contracts into a 

 spire. 



1 have said that in Corydalis claviculata the end of the leaf or 

 the tendril (for this part may be indifferently thus designated) does 

 not contract into a spire. The branchlets, however, of the ten- 

 dril, after they have wound round thin twigs, become deeply 

 sinuous or zigzag ; and this may be the first indication of the 

 process of spiral contraction. Moreover the whole end of the 

 petiole or tendril, if it seizes nothing, ultimately bends abruptly 

 downwards and inwards, showing that its inferior surface con- 

 tracts ; and this may be confidently teoked at as the first indica- 

 tion of the power of spiral contraction. For with all true ten- 



^ 



drils when they contract spirally, it is the lower surface, as Mobl 



(S 



If the inferior surface of 



