116 HE, DAItAVIX ON CLIMBING IM.AMS. 



Secondly, if the young shoot of a twining plant, or if a tendril, 

 be placed in an inclined position, it soon bends upwards, though 

 completely secluded from the light. The guiding stimulus to this 

 movement is no doubt the attraction of gravity, as Andrew Knight 

 showed to be the case with germinating plants. If a succulent shoot 

 of almost any plant be placed in an inclined position in a glass of 

 water in the dark, the extremity will, in a few hours, bend upwards ; 

 and if the position of the shoot be then reversed, the now downward- 

 bent shoot will reverse its curvature ; but if the stolon of a Straw- 

 berry, which has no tendency to grow upwards, be thus treated, 

 it will curve downwards in the direction of, instead of in opposi- 

 tion to, the force of gravity. As with the Strawberry, so it is gene- 

 rally with the twining shoots of the llibhertia dentata, which climbs 

 laterally from bush to bush ; for these shoots, when bent down- 

 wards, show little and sometimes no tendency to curve upwards. 



Thirdly, climbing plants, like other plants, bend towards the light 

 by a movement closely analogous to that incurvation which causes 

 them to revolve. This similarity in the nature of the movement was 

 well seen when climbing plants were kept in a room, and their first 

 movements in the morning towards the light, and their subsequent 

 revolving movements, were traced on a bell-glass. We have also 

 seen that the movement of a revolving shoot, and in some cases of 

 a tendril, is retarded or accelerated in travelling from or to the 

 light. In a few instances tendrils bend in a conspicuous manner 

 towards the dark. Many authors speak as if the movement of a 

 plant towards the light was as directly the result of the evapora- 

 tion or of the oxygenation of the sap in the stem, as the elongation 

 of a bar of iron from an increase in its temperature. But, seeing 

 that tendrils are either attracted to or repelled by the light, it is 

 more probable that their movements are only guided and stimu- 

 lated by its action, in the same manner as they are guided by the 

 force of attraction from or towards the centre of gravity. 



Fourthly, we have in stems, petioles, flower-peduncles, and 

 tendrils the spontaneous revolving movement which depends on 

 no outward stimulus, but is contingent on the youth of 1 ho part 

 and on its vigorous health, which again of course depends on pro- 

 per temperature and the other conditions of life. This is perhaps 

 the most interesting of all the movements of climbing plants, be- 

 cause it is continuous. Very many other plants exhibit sponta- 

 neous movements, but they generally occur only once during the 

 life of the plant, as in the movements of the stamens and pistils, 

 &c, or at intervals of time, as in the so-called sleep of plants. 



