ON THE MOTIONS OF THE TENDRILS OF PLANTS. 16? 



horizontally; when their tendrils gradually descended beneath their 

 stems, with which they ultimately stood very nearly at right angles.; 



A third set of plants were trained almost perpendicularly downwards ; 

 but with an inclination of a few degrees towards the north ; and the 

 tendrils of these permanently retained very nearly their first position, 

 relatively to their stems ; whence it appears that these organs, like the 

 tendrils of the ampelopsis, and the claws of the ivy, are to a great extent 

 under the control of light. 



A few other plants of the same species were trained in each of the pre- 

 ceding methods ; but proper objects were placed, in different situations, 

 near them, with w hich their tendrils might come into contact ; and I was 

 by these means afforded an opportunity of observing, with accuracy, the 

 difference between the motions of these and those of the ampelopsis, 

 under similar circumstances. The latter almost immediately receded 

 from light, by whatever means that was made to operate upon them; and 

 they did not subsequently show any disposition to approach the points, 

 from which they once receded. The tendrils of the vine, on the contrary, 

 varied their positions in every period of the day, and after returned 

 again during the night to the situations they had occupied in the pre- 

 ceding morning ; and they did not so immediately, or so regularly, bend 

 towards the shade of contiguous objects. But as the tendrils of this 

 plant, like those of the ampelopsis, spring alternately from each side of 

 the stem, and as one point only in three is without a tendril, and as each 

 tendril separates into two divisions, they do not often fail to come into con- 

 tact with any object within their reach ; and the effects of contact upon the 

 tendril are almost immediately visible. It is made to bend towards the 

 body it touches, ^nd if that body be slender, to attach itself firmly by twin- 

 ing round it, in obedience to causes which I shall endeavour to point out. 



The tendril of the vine, in its internal organization, is apparently 

 similar to the young succulent shoot and leaf-stalk, of the same plant ; and 

 it is as abundantly provided with vessels, or passages, for the sap ; and 

 I have proved that it is alike capable of feeding a succulent shoot, or a 

 leaf, when grafted upon it. It appears therefore, I conceive, not impro- 

 bable, that a considerable quantity of the moving fluid of the plant, passes 

 through its tendrils : and that there is a close connection between its 

 vascular structure and its motions. 



I have proved in the Philosophical Transactions of 1806, that centrifu- 

 gal force, by operating upon the elongating plumules of germinating seeds, 

 occasions an increased growth and extension upon the external sides of 

 the young stems, and that gravitation produces correspondent effects ; 



