PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
255 
body is put in contact with the external surface of a tendril in its straight form, it 
does not curl round the body which excites the movement, but on the contrary from 
the outside inwards, although there is nothing there for it to embrace. 
This tendency to curl only on one side has induced me to examine the tendrils, to 
see whether I could discover by means of the mieroscope a special anatomical 
structure that might explain this peculiarity. 
I have made observations with the microscope of Amici and a magnifying power 
of 800 times on very thin slices of the tendril, taken some from the external, and 
some from the internal side. When the specimens were cut out of tendrils already 
contracted in a spiral form, the only visible difference was that the cells on the in- 
ternal side appeared very little elongated and almost square ; while, on the contrary, 
they were much narrower and longer on the opposite side. But this appearance was 
evidently meehanical and produced by the contraction itself ; for when I examined 
slices cut in all directions from tendrils still in their straight form and not con- 
tracted, I found the anatomical structure to be preeisely the same in all, and indeed 
similar to that of those leafstalks of the same plant which are not susceptible of 
being curled up. 
I caused a straight tendril of Tainus to curl by the excitement occasioned by the 
touch of a pencil. Two knots were closely tied within the spaee of ten minutes. 
I then cut out the tendril near its base, so as to interrupt its communication with 
the plant ; the tendril, though kept in the light and in a warm and damp atmosphere, 
did not continue to curl itself. 
When a straight tendril of Tamus is placed in a tumbler full of water, so as 
not to touch its edges, it does not experience any contraction, but is just as ready as 
before to curl up by the first contact of any solid body. 
I have immersed a tendril many times over in a solution of gum-arabic, leaving 
it to dry between each successive immersion, so as to form round it a thin coat ; the 
tendril so covered had not in any degree lost its power of contraction by the contact 
of a solid body, and the coat of gum did not seem to prevent the close adherence 
of the knots. 
Liquid ammonia in a diluted state has no influence on tendrils. Alcohol and 
eau de Cologne seem to possess a slight exciting influence on the contraction of 
tendrils, which are thereby bent in the form of a bow, but do not continue to curl, 
and they appear not to experience any bad effects. When immersed, with the same 
precautions, in sulphuric acid diluted with water, the tendril contracts itself imme- 
diately and energetically. It curls up in a spiral form, though there be no object 
present round which it might roll itself. The knots, at first very loose, continue to 
tighten up to a certain point, although there always remains an empty space in the 
middle of the rings. After some time, the part touehed by the acid becomes dis- 
organized and dries up. 
Diluted nitric acid has the same effect as sulphuric acid, but the contraction is 
