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XVIII. On the Direction assumed by Plants. By Professor Macaire of Geneva. 
Communicated by P. M. Roget, M.D., Sec. R.S. 
Received June 17, — Read June 17, 1847. 
§ 1 . On the Curling-up of Tendrils. 
The plants with tendrils are very numerous. According to Mr, Palm there are 
about five hundred^ divided into seventeen families. Of these, one hundred and sixty 
have a ligneous stem, eighty-three are perennial herbs, and one hundred and seventeen 
are annuals. 
My experiments on the mode of curling-up of these organs were made on the ten- 
drils of the Tamus communis*, a plant of the family of the Asparageae. The tendrils 
of this plant seem to be a thread-like degeneration of the footstalk of a leaf, whose 
place they occupy on the stem of the plant. They are at first straight, and are im- 
planted perpendicularly on the stem, so as to form almost a right angle with it ; the 
extreme end of the tendril only has a slight tendency to bend towards the stem. 
When the tendril of the Tamus is touched by any solid body whatever on a point of 
its surface not too far from the extremity, it contracts itself from the outside inwards, 
forming at first a hook and then a curl, so as to embrace the body closely if that body 
be circular ; if angular, the knot is only tight on the angles, and bulges out on the 
surfaces. When a first knot is tied, the end of the tendril continues to roll itself up 
in a coil, though not in contact with the body in that part, and the coil slides over 
the external object, coming nearer and nearer to it so as to embrace it several times : 
in the mean while, the other end of the tendril continues also to contract itself. In 
this way as many as seven or eight knots are formed. I have frequently seen three 
tied before my eyes within the space of a quarter of an hour on a metallic wire, small 
branches of wood, a pencil, my finger, &c. The contact of any solid body whatever 
is sufficient to produce this effect ; so much so, that although the tendril is evidently 
destined by nature to support the creeper to which it belongs, by means of the sur- 
rounding plants, yet if it chances to meet a part of the very same plant of Tamus of 
which it is itself a portion, the contact causes it immediately to roll itself up around 
that portion. 
* Since this paper was read the author has been informed that Tamus communis is a plant without tendrils. 
The plant on which he made the experiments here referred to is a common weed in the gardens in Switzerland. 
Being without the means in this country of identifying it, he must supply the information on a future occasion, 
only adding that Smilax aspera, another of the Asparageae, has been suggested to him as being probably the 
plant. 
2 L 2 
