418 JOURNAL OF SCIENCE. 
by increase in thickness. Spirals thus formed tend to draw the slack 
parts of the plants upwards. This must be considered a very much 
higher development than that which is found in the lawyer. 
In the hop, french bean, and many other plants, the stems 
support themselves by twining round stronger plants. This is 
no accidental mode of growth, but is in obedience to a law 
very deeply ingrained in the different species. Whenever a 
young stem of a twining plant attains a length of a few inches, 
it begins to go through a periodical revolution, performing a 
more or less circular swinging movement. If in the course of 
this revolution it comes into contact with a stick or stem or other 
resisting agent, the movement of the lower portion is arrested while 
the upper part moves on more rapidly than before, twining round and 
round the support. Sometimes of course when twiners, such as 
french beans, don’t come into contact with suitable supports, they 
twine round one another, and almost exemplify the proverb of the 
blind leading the blind and both falling into the ditch. A curious 
feature of this twining movement is that it invariably follows the 
same direction in the same species. Thus the hop always twines 
from right to left, and the french bean from left to right of the 
observer viewing the coil from the outside. The lower parts of 
the stems of these plants may be tied in the reverse direction 
many times, but the end of the stem as soon as it is liberated, 
returns to its original method of twining. The hop in addition 
to its twining powers, developes all along its epidermis small 
hooked tubercles which point downwards, and these exercise a 
wonderful grasp on a rough stem or branch. ‘These tubercles 
enable the climbing stem to slip up a support, but they prevent 
it coming down. 
Leaving out of account another set of climbers, viz., root-climbers, 
like the Ivy, which develope a special kind of roots for the purpose of 
clasping supports, I must pass on to consider the last and most highly 
developed form of climbers, those, namely, which like the pea, form 
tendrils. These organs may be modified branches, leaves, or stipules. 
In the pea, as I formerly pointed out, the leaflets, with the exception 
of the two lowest, have all become modified into tendrils. These 
tendrils are sensitive to the slightest touch, so that if rubbed even 
with a feather on one side, they will come round in the direction from 
which the irritation comes. Of course if the irritation be caused by a 
twig against which the pea is moved by the wind, the tendril quickly 
turns round and round it, thus securing fast hold. In addition to 
their sensitiveness to touch or pressure, tendrils perform a regular 
rotatory movement similar to that performed by the free points of 
twining stems.. Were they to make a complete revolution they would | 
of course catch hold of their own stem, but this is avoided by their 
sweeping round half a circle, then rising up gradually to a nearly 
perpendicular position, passing the stem, and again falling to the 
horizontal to resume the sweeping. movement. There are, of course, 
innumerable degrees in the perfection to which tendrils have attained. 
But there can be no doubt as to the fact that tendril bearers are much 
more highly developed than mere twiners. The habit of performing 
a rotatory swinging movement is so common in plants, that we may 
consider the habit of twining as very much older in point of develop- 
