242 
ening of the relatively rigid curving organ to take place, when 
it is placed in a plasmolysing solution, or in alcohol and 
then in water. The actual curvature can therefore in such 
cases only be stated to be due to heterauxesis or inequilateral 
growth, without any further precision of the modus operandi, 
or of the causes directly influencing growth, being possible. Any 
tendency, which the meristematic cells of the concave side 
may have, to increase their turgidity above that of those on 
the concave side, is apparently counterbalanced by their more 
rapid growth and division; whilst the rigidity of the other 
tissues is such, that trifling differences of turgidity are unable 
directly to perceptibly affect the curvature of the adult organ. 
In analogy with other irritable organs, it seems more ratio- 
nal and correct to regard the irritable hook (or tendril) as an 
organ, which responds as a whole, when any part is stimula- 
ted, though the result produced will naturally, in both posi- 
tion and amount, correspond to and be affected by, the nature 
and point of application of the exciting stimulus. Feeble localized 
stimulation may, provided any result at all is noticeable, produce 
an effect perceptible only over the region directly stimulated. 
The irritability to contact stimulation alone, in the strict 
sense of the term, is localized mainly or almost entirely on 
the concave surfaces of the hooks. When the pressure is suffic- 
ient to produce pronounced internal mechanical strain, whether 
it is constant or variable, at whatever point it is applied, a 
perceptible result is finally produced , if any response at all is 
possible, though the end result is more marked and more rapidly 
produced, when normal conditions of contact are assured. 
DESCRIPTION OF PHOTOGRAPHS, 
Pl. XVIII and XIX, 
1. Strychnos laurina, Attached and unattached hooks-tendrils. 
2. Artabotrys Blumei. On the right the hooks bear flowers 1), 
8. Bauhinia tomentosa. Hook like tendrils, 
. - Dalbergia linga. Palvini grasping support. The curvature of the pulvinus * is 
mporary one caused by rubbing just before the photograph was taken. 
1) Erroneously named on plate XVIII Ancistrocladus Vahlii. 
Sk seca sh vena ey iG ‘ 
Beene: jee Sinan er iret atte teers Cee cS hb 
