MODIFICATIONS OF FORM 



215 



B 



its straggling habit, partly by the spread of its pulpy fruits by birds. The 

 widely spreading branches bear hooked prickles on their projecting angles, 

 which are effective in aiding support (iii). In other cases hooks that help the 

 straggling are produced from other parts. The climbing Rattan Palms of the 

 genus Calamus bear them on the concave side of the whip-like leaf-apices, 

 or of the axillary buds ; for it is sometimes 

 the one, sometimes the other, which serves 

 in this genus as the climbing organ (iv.). 

 In the Jujube (Zizyphus) there are woody- 

 stipules to the leaves which are borne by 

 the curved, whip-like branches. Of these 

 stipules the one that is downwardly- 

 directed of each pair is sharply reflexed, 

 while the other points forwards (ii.). A 

 parallel is seen in Sageretia, but in this case 

 it is the axillary buds that are effective, 

 for the lower of each pair forms a recurved 

 hook, while the upper develops upwards 

 as a leafy shoot, (i.) The mechanical effect 

 is exactly the same as in the Jujube, but 

 the parts used are different. In the 

 Palm Desmonchus, it is the distal pinnae 

 that are reflexed, and act almost like the 

 flukes of a patent anchor (vii.). A very 

 similar mechanical effect is shown by the 

 reflexed axillary branches of Carissa (v. vi.). 

 Such examples illustrate in what varied 

 ways straggling may be made an effective 

 method of support. They involve such 

 diverse parts as emergences, stipules, pinnae, 

 and axillary branches. In fact any part 

 of the shoot-system may be used. The 

 instances come from most diverse families 

 of Dicotyledons and Monocotyledons. 



: ii:. > 



Fig. 144- 



Climbing by prehensile methods has 



• ,1 r Twining stems. A , Sinistrorse shoot of 



gained more attention than straggling, Pharbit i S b Dextrorse shoot of Myrsi- 

 because it is so well represented in the #**«. (After strasburger.) 

 Native Flora, and because the advantages which it brings are so 

 obvious. The attachment to the support may be by a twining stem, 

 the Hop, Scarlet Runner, or Convolvulus; or by tendrils of 



as in 



various sorts, and by prehensile leaves. The twining of a stem is 

 partly due to the execution of circumnutatory movements by the 

 apical part of the stem, the sweep of the nutatory spiral being greatly 

 increased by the horizontal or oblique orientation which the upper 

 part of the stem assumes. If the stem comes in contact with an up- 

 right support of suitable thickness it laps round it with a continuous 



