106 TWINING PLANTS [CH. 



side of the climbing shoot which touches the support is so 

 acted upon by the contact that it grows still more slowly 

 than the outer free convex side, and the stem now twines 

 round the vertical stick or other support, the at first loose 

 and flat coils becoming steeper and tighter later on, as 

 the then older parts try to erect themselves more and 

 more. 



Most twiners coil in the direction opposite to that of 

 the hands of a watch e.g. Convolvulus, Kidney Bean, 

 Pharbitis, Akebia, Wistaria, Ipomcea, Aristolochia, Aspa- 

 ragus, &c. 



Nevertheless there are many which invariably twine 

 in the opposite direction e.g. the Hop, Honeysuckle, 

 Jasminum, Polygonum, Plumbago, Clerodendron, Thun- 

 bergia, Tamus, Lapageria, &c. 



While nothing is known of the importance or meaning 

 of the direction of the coiling, it is interesting to note 

 Darwin's observations that several plants, e.g. Loasa 

 aurantiaca, Scyphantlms elegans, and the occasional 

 twiner Solatium Dulcamara, coil in both directions alter- 

 nately, i.e. the direction of twining is reversed after a few 

 turns in any one direction. The same occurs in Blumen- 

 bachia, Hibbertia, Testudinaria sylvatica, Ipomcea jucunda, 

 and some others. 



Many twining stems are quite smooth, e.g. some species 

 of Convolvulus, Bowiea, Tamus, &c., but others have hairs 

 (Hoya, Buttneria), bristles (lodes ovalis, Tetracera), or 

 reversed barbs (Polygonum, Capparis Roxburghii, Ipomcea 

 muricata), or hooks of various kinds (Hop), these and the 

 ridges sometimes found are possibly of service in giving a 

 firmer hold. These ridges must not be confounded with 

 the twist-ings or torsions which climbing stems undergo 

 after coiling round the support. The torsions are pro- 

 duced partly by the friction on the support as the coils 



