<3i MR. DAHWTN OX CLIMBING PLANTS. 



many trials with black and white glass and cards to prove it, but 

 failed from various causes ; yet these trials countenanced the 

 belief. The tendril may be looked at as a leaf split into filaments, 

 with the segments facing in all directions ; hence, when the revolv- 

 ing movement is arrested, so that the light shines on them 

 steadily In one direction, there is nothing surprising in their 

 upper surfaces turning towards the light : now this may aid, but 

 will not account for, the whole movement ; for the segments would 

 in this ease move towards the light as well as turn round to it, 

 whereas in truth the segments or branches of the tendrils not only 

 turn their upper surfaces to the light, and their lower surfaces 

 which bear the hooks to any closely adjoining opaque object (that 

 is, to the dark), but they actually curve or bend from the light 

 towards the dark. 



When the Coha^a grows in the open air, the wind must aid the 

 extremely flexible tendi-ils in seizing a support, for I found a mere 

 breatb sufficed to cause the extreme branches of a tendril to catch 

 by their hooks twigs which they could not have reached by the 

 revolving movement. It might have been thought that a tendril 

 thus hooked only by its extremity could not have fairly grasped its 

 support. But several times I watched cases like the following, 

 one of which alone I will describe : a tendril caught a thin stick 

 by the hooks of one of its two extreme branches ; though thus 

 held by the tip, it continued to try to revolve, bowing itself out to 

 all sides, and thus moving its branches ; the other extreme branch 

 soon caught the stick; the first branch then loosed itself, and 

 then, arranging itself afresh, again caught hold. After a time, from 

 the continued movement of the tendril, a third branch became 

 caught by a single extreme hook ; no other brandies, as things then 

 remained, could possibly have touched the stick ; but before long 

 the main stem, towards its extremity, began just perceptibly to 

 contract into an open spire, and thus to shorten itself (dragging 

 the whole shoot towards the stick), and as it continued to try to 

 revolve, a fourth branch was brought into contact. As the spiral 

 contraction travelled down the main stem and down the branches 

 of the tendril, all the lower branches, one after another, were 

 brought into contact with the stick, and were wound round it and 

 round their own branches until the whole was tied together in an 

 inextricable knot round the stick. The branches of a tendril, 

 though at first so flexible, after having clasped a support for 

 a time, become rigid and even stronger than they were at first. 

 Thus the plant is secured to its support in a perfect manner. 



