434 



Of the Penetration of a Hemisphere by an indefinite Number of equal 

 and similar Cylinders. By Thomas Knight, Esq. Communicated 

 by Sir Humphry Davy, LL.D. Sec. R.S, Read March 19, 1812. 

 [Phil Trans. 1812,^.310.] 



The problem which Mr. Knight here undertakes to solve, is to 

 pierce a hemisphere perpendicularly to the plane of its base, with 

 any number of equal and similar cylinders of such kind, that after 

 the removal of these cylinders, the remainder of the hemisphere 

 shall admit of exact cubature ; and when the surface has been thus 

 perforated, the remaining surface shall admit of exact quadrature. 



But the solution of this problem, as well as of those contained in 

 the preceding communication, was, of course, such as not to admit 

 of being publicly read. 



On the Motions of the Tendrils of Plants. By Thomas Andrew Knight, 

 Esq. F.R.S. In a Letter to the Right Hon. Sir Joseph Banks, Bart. 

 K.B. P.R.S. Read May 4, 1812. [Phil Trans. 1812, p. 314.] 



Some naturalists have supposed tendrils to be endued with some 

 degree of perception, to which their propensity to approach neigh- 

 bouring objects may be ascribed ; and though others who have written 

 on the same subject may have rejected this hypothesis, it does not 

 appear to Mr. Knight that any direct experiments have been made 

 similar to those which he here describes, for the purpose of ascertain- 

 ing whether these motions may not be ascribed to peculiarity of or- 

 ganization, aided by the operation of external causes. 



The plants selected for his experiments were, the Virginia Creeper, 

 the Ivy, the Vine, and the Pea. When a young plant of the creeper, 

 trained directly upwards, was placed alone in the centre of a forcing- 

 house, its tendrils were all turned towards the north wall ; but as this 

 was out of their reach, they declined gradually, and ultimately fixed 

 themselves on the upright stem beneath and upon its support. 



When other plants were placed near the glass, their tendrils were 

 always directed from the light, as in the former instance, although 

 no object was within their reach on the dark side. 



Mr. Knight next tried the effect of placing near them a piece of 

 dark paper; to this they appeared to be strongly attracted, and 

 when the paper was removed to a new position, the tendrils were 

 found to follow it. When a piece of glass was substituted for the 

 paper, the tendrils showed no disposition to approach it ; but, on the 

 contrary, when it was placed so as to reflect the light of the sun upon 

 the tendrils, they appeared to be strongly repelled by it. 



In making corresponding experiments on the ivy, Mr. Knight found 

 the same propensity in its claspers to recede from the light ; but it 

 was necessary to place substances much nearer than in the former 

 experiments for them to manifest any appearance of spontaneous 

 motion. 



When a young plant of the vine was placed under the same cir- 



