22 MR. DAttWIN ON CLIMIiiNG PLANTS. 



thickness, yet at Kew a plant ascended a trunk above G inches in 

 diameter. The tropical twiners, on the other hand, can ascend 

 thick trees. I hear from Drs. Thomson and Hooker that this is 

 the case with the Btitea parvijlora, one of the Menispcrmacea?, 

 and with some Dalbergias and other Leguminosa). This power 

 would evidently be almost necessary for twining plants inhabiting 

 tropical forests, as otherwise they could hardly ever reach the 

 light. In our temperate countries twining plants which die down 

 every year to the root would suffer if they were enabled to twine 

 round trunks of trees, for they could not grow tall enough in a 

 single season to reach the summit and gain the light. 



By what means some twining plants are adapted to ascend only 

 thin stems, whilst others can twine round thick trees, I do not 

 know. It appeared to me probable that twining plants with very 

 long revolving shoots might be able to ascend thick supports ; 

 accordingly I placed Ceropcgia Gavdnerii near a post G inches in 

 diameter, but the shoots entirely failed to wind round it; their 

 length and power of movement apparently serving merely to find 

 some distant but thin stem round which to twine. The Splucro- 

 stemma marmoratum is a vigorous tropical twiner, and as it is a 

 very slow revolver, I thought that this latter circumstance might 

 aid it in ascending a thick support ; but though it was able to 

 wind round theG-inch post, it could do this only on the same level 

 or plane, and could not ascend in a spire. We can, however, see, 

 in accordance with the views previously explained, that a re- 

 volving shoot, which, after coming into contact with any support, 

 quickly lost its power of movement, would not again be drawn 

 away from its support by the returning or opposite movement, 

 and therefore remaining in contact with it, might thus ascend 

 a thick support. But whether this slight difference in retaining 

 for some time or in quickly losing the power of movement after 

 coming into contact with a support alone determines how thick 

 an object the stem can ascend I do not know. 



As ferns differ so much from phanerogamic plants, it may be 

 worth while here to show that twining ferns act in no respect 

 differently from other twining plants. In Lyrjodium articulatum 

 the two internodes first formed above the root-stock did not move ; 

 the third from the ground revolved, and at first very slowly. This 

 species is a slow revolver : but L. scandens made five revolutions 

 at an average rate of 5 h. 45 m. ; and this represents fairly well the 

 usual rate, taking quick and slow movers, amongst phanerogamic; 

 plants. The rate was accelerated by increased temperature. The 



