Mr. Knight’s Experiments on 
344 
in some degree, requisite; (for plants have always appeared to 
me to thrive best with moderate variations of temperature ;) but 
the immediate cause will, I think, be found in an intrinsic power 
of producing motion, inherent in vegetable life ; and 1 hope to 
be able to point out an agent, by which the mechanical force 
required may possibly be given. 
There is, you know, in every kind of wood, what workmen 
call its grain, consisting of two kinds, the false or bastard, and 
the true or silver grain. The former consists of those concentric 
circles which mark the annual increase of the tree; and the 
latter is composed of thin laminae, diverging in every direction 
from the medulla to the bark, having little adhesion to each 
other at any time, and less during the spring and summer, than 
in the autumn and winter; whence the greater brittleness of 
wood in the former seasons. These laminae (which are of 
different width in different kinds of wood) lie between, and 
press on, the sap-vessels of the alburnum : they are visible in 
every wood that I have had an opportunity to examine, except 
some of the palm tribe ; and these appear to me to have pecu- 
liar organs, to answer a similar purpose. If you will examine a 
piece of oak, you will find the laminae I describe; and that every 
tube is touched by them at short distances, and slightly diverted 
from its course. If these are expansible under changes of tempe- 
rature, or from any cause arising from the powers of vegetable 
life, I conceive that they are as well placed as is possible, to 
propel the sap to the extremities of the branches; and their restless 
temper, after the tree has ceased to live, inclines me to believe, 
that they are not made to be idle whilst it continues alive. 
I shall at present confine my observations to the English 
oak, though the same are applicable, in a greater or less degree, 
