274 
»JOTlONS IN PLANTS. 
Real cause. 
Various ten 
driis twine 
\.itiiin the 
plant. 
Curious ten- 
drils taken for 
perspiration. 
that the increase of one part would contract the other ; but I 
believe it ’will be found, that the tendril hardly ever fails to turn 
htf'ore the stick touches it ; and I am sure, that the vessels are 
all longitudinal ones, and cannot, therefore, send their juices 
to the other side without twisting and spoiling the tendril, and 
therefore becoming incapable of turning ; whereas all the 
motion explained by Mr. Knight may be effected by a spiral 
wire taken out of its case, and exposed to the atmosphere. It 
will turn to the part from which the light proceeds, change its 
side as the light is altered, and be equally repelled by a black, 
ordrawm by a white paper j and as all that remains of the 
plant, when the spiral wire is taken from it, is perfectly inert, 
there can, I think, be no doubt, that it is the spiral wire that 
causes its motion. Examine the tendril of the cucumber 
when it first appears, with all its buds in their aggregate state ; 
it never varies from the figure, fig. 5, and yet it can have been 
subject to no pressure, nor turned round any form. The vine 
runs on an inch or two straight, and then changes its direction, 
when, if it does not meet any thing round which to twine, it 
forms its first circle at the point, and then runs up into a long 
spiral exactly resembling the muscles of the plant, and turning 
the same ivay. Why does the convolvulus arvensis so trouble 
gardeners ? because it strangles each plant ; its slender stalk 
twines round each flower like a tendril, and the convulsive move- 
ment is caused by the quantity of spiral wire conquering the 
rest of the stalk, and making it obey the natural direction of 
the muscles. It is almost the same by the black bryony j 
but, if dissected with care, the tendrils will be found within 
the cuticle, already curled. But, what is still more convincing, 
view the backs of innumerable leaves, particularly the phascolus 
vulgari, on which are found a quantity of hairs of the tendril 
kind, attended with a sort of instrument in the shape of a bot- 
tle, of which I shall give a sketch. Not one of them sur- 
rounds an object, yet they all wind in a perpetual circle j (see 
fig. 7) and, as they are perfectly clear, the spiral wire may be 
seen winding through them, directing their figure and guiding 
their motion. These w'ere formerly taken for perspiration. 
By 
