1852.] OF THE ROYAL INSTITUTION. 197 
Ino and Bacchus — Little Nell—Psyche, in Cheverton’s Machine 
Sculpture. [Exhibited by W. T. Copeland, Esq.] 
Partridge and Woodcock, worked in Leather, in imitation of Wood- 
Carving, by Mr. W. Sanders. 
Portraits of John Dalrymple, Esq., F.R.S. and of Dr. Holland, F.R.S., 
by J. Z. Bell, Esq. 
Mr. C. Varley exhibited several interesting objects by the Micro- 
scope. 
WEEKLY EVENING MEETING, 
Friday, May 14. 
Sir Cuarwes Fexttows, Vice-President, in the Chair. 
Tue Rev. Epwin SIpNeEy, 
On the Rise of the Sap in the Spring. 
Arter a few prefatory observations, the speaker divided the subject 
into four parts which he proposed to consider in order. 1. A 
short description of certain physical phenomena to be regarded as 
preparatory. 2. Their application to the known organism of vege- 
table structures. 3. The circumstances under which these organisms 
will be called into that activity which may be regarded as the 
proximate cause of the rise of the sap in the spring. 4. The 
diffusion of the sap through the plant. The inquiry was limited 
of course to plants of our own climate. 
1. In directing attention to the first part of the subject, it was 
observed-that vitality must not be disregarded. The most chemical 
and physical forces fail to explain all. Vital force is mysterious, it is 
true, but so are all forces. If there were nota living formative force su- 
peradded above dead physical forces, all the varieties of organized sub- 
stances could not originate as they do from a simple vesicle. The phe- 
nomena now to be considered were those of capillarity and endosmosis. 
The former is greatly affected by temperature, and the imbibition due 
to it differs much in different liquids and solutions. Endosmosis is 
known as the phenomenon of the mixture of two liquids of unequal 
density through a membrane, accompanied by a change of volume. 
It is called endosmosis when the volume increases, exosmosis when 
it diminishes. It is generally, but not always, found that when the 
heavier liquid is above the lighter, mixture is accelerated by the 
interposition of the membrane. Other things equal, the force of 
the current varies as the excess of the density of the interior 
liquid propertional to water. A current with a pressure of several 
