336 
AMERICAN HOMES AND 
GARDENS 
September, Ig1I 
Clematis, a stalk-climber 
striking instances. Certainly the most curious point about 
these plants which twist up supports by means of their 
stems is the constancy with which they will adhere to their 
peculiar mode of growth. Owing to this strange habit the 
twining species fall naturally into two classes from which 
there is no variation: those which twist from left to right 
like the hands of the clock, and those which travel in an 
opposite direction. Of the former the Hop is a good 
example, while of the ‘latter there is no better instance 
than the Bean. Strangely enough, there are no possible 
means by which these twining plants may be coerced or 
caused to change the course which has been allotted to 
them. Just why they should be so constant to the one 
direction it must be admitted that no explanation can be 
offered. 
A modified form of circumnutation is to be seen in the 
case of those plants which climb by means of their leaf- 
stalks. Of these we shall find excellent instances in the 
garden Tropaeolum and the several species of Clematis. 
As a general rule it is to be observed that the stalks of 
the foliage develop on ordinary lines until they come into 
Bean and hop 
A twining clematis 
contact with any support. ‘This irritation seems at once to 
bring into action a latent twisting tendency causing the 
stalk to twine itself around the object and thus secure a 
hold. Meanwhile the leaf itself carries out its normal 
duties without being in any way affected by the office which 
the petiole is performing. It is very often the case that 
the leaf-stalks of these plants twine around one another 
and in this way the subject is able to dispense with any 
outside help at all. 
The root climbers form a most interesting group which 
by means of adventitious processes are able to rise with the 
greatest ease. One of the most common examples is that 
of the Ivy, a plant which produces an abundance of root- 
lets on the under side of its stems when occasion requires. 
These, owing to the minute hairs with which they are sup- 
plied, are able to adhere to surfaces offered by brickwork, 
or the trunks of trees. A curious feature of the Ivy shoots 
is the fact that they are endowed with the property known 
as negative heliotropism—that is, a tendency to grow away 
from the light. It will be realized that this characteristic 
causes the shoots to press closely against any support, and 
Ampelopsis climbing by adhesive discs 
The passion flower 
Ivy climbing by roots 
