PHYSIOLOGY. ! 221 
die, chiefly in the wood. This seems’ to: arise from 
a change in its chemical component parts. It is well 
known that wood when moistened expands, and 
when dry contracts, 
Formerly it was thought that Jina au gTOW 
in breadth only by snpetod of the vinterstices be- 
tween the’fibres of the wood, when moisture per- 
vades them. Mr De Luc, however,. has shown, 
that the fibres themselves may be elongated, though 
in a small degree, and again contract. And 
has made the singular remark, that box-wood con- 
tracts its fibres longitudinally when moist, but clon- 
gates them in a dry atmosphere. It however un- 
dergoes the changes in breadth in the same manner 
as other wood. He examined a great number of 
different sorts of wood, but not a single one shew red. 
the phenomenon of boxwood. 
It is this contractility of wood, which in econo- 
mical and technical use, is often followed by most 
unpleasant consequences; and, it is on this‘account 
that wood 1s subjected to different processes, by 
which its contractility is entirely lost. 
The dry stalks of Anastatica hierechuntica, known 
under the name of the rose of Jericho, and the seed 
vessels of the genus Mesembryanthemum, or as 
gardeners call it, the Candian flower, retain this 
power very long, expand in water, on contract 
when dry. The same happens with the Algae and 
Mosses, and with the calyx of Carlina vulgaris. 
: Many of these parts may serve as Hygrometers. 
All plants are possessed of 77 ae y, though not 
bow 
ed 
CD 
‘in the same degree., ‘The leaves of Mimosa pudica, 
By yg 
ye  SbnSILIVa, 
