CLIMBING PLANTS OF THE SOUTH MIDLANDS. 
63 
changes of temperature. When external conditions are favourable 
the circular nutation of the free apex is usually uniform. In the 
hedge bindweed, Convolvulus septum, Darwin records 1 hour 
42 minutes as the time occupied in effecting one revolution, 
and in the garden bean, Phaseolus vulgaris , 1 hour 55 minutes. 
The torsion of the stem is quite distinct from circular nutation, 
although they coincide in direction. This correspondence is con¬ 
spicuous in the hop and the honeysuckle, but in the latter it is 
much more pronounced in the primary axes than in the branches 
given off by them. Torsion is apparently imparted to the older 
internodes in order that they may be strengthened and thus enabled 
to support the younger portions until the apex has secured a point 
of attachment. When contact with a supporting medium has 
been effected, growth becomes vigorous, and formative materials 
are copiously supplied to the organs that are thus performing their 
legitimate functions. When the black bryony has overtopped 
a hedgerow, and thus raised itself above other means of support, 
several stems twine round each other and form a cable, which 
enables them to rise still higher, until they bend down by the 
weight of their own growing parts. 
Stems, in twining round suitable supports, move either to right 
or to left, and all the species of the same genus usually assume the 
same habit, or rather they exhibit hereditary tendencies, which are 
due to common ancestry. Those that move from left to right, that 
is, with the sun, or with the hands of a watch, are described as 
sinistrorse, while those that move in a contrary direction, that is, 
right to left, are said to be dextrorse. 
Of the latter, familiar examples are furnished by the hop, 
honeysuckle, black bryony, black bindweed, and the bittersweet. 
Of the last mentioned, Darwin remarks that “the habit is not 
constant.” 
The bittersweet is shrubby in habit, and is better able to support 
its own weight .than the others just enumerated. Consequently 
the climbing habit is not so strongly developed as in the other 
twining plants of this district. It is most marked in plants of this 
species that have a slender habit resulting from growing in company 
with tall herbage. When occurring in open situations they are 
more compact, and occasionally several stems form a slightly 
twisted cable. 
The wild honeysuckle, which is common in this district, is 
frequently found growing in company with hazel. It sometimes 
happens that a primary stem of honeysuckle attaches itself to 
a vigorously growing shoot of the latter. The tension of the honey¬ 
suckle upon the tissues of the hazel becomes very pronounced as 
the growth of both proceeds. An illustration of this was observed 
in a thicket at Woodside, Beds, in January, 1904. The hazel 
stem had attained a diameter of nearly two inches, whilst that of 
the honeysuckle was half an inch. The constriction of the latter 
upon the former was so great, that a considerable swelling was 
produced where the two were united, which showed as a sinuous 
