1852.] OF THE ROYAL INSTITUTION. 199 
taught that for every grain of solid matter fixed in the plants tried 
when healthy, two hundred grains of water passed through by evapo- 
ration. Capillarity due to the ducts must also be taken into account 
in the rise of the sap. As regarded its rise in the spring, when the 
vigorous movement so well known takes place, a distinct explanation 
could be given. Hereseveral experiments of Hales were mentioned as 
examples of ingenious method, but the true inferences could not be 
made at that time for want of knowledge. The quiescence in winter is 
due to the way in which evaporating surfaces are closed, and even 
sealed up, so that capillarity, which does not take place in sealed tubes, 
cannotact. The cells of buds are then filled with thin fluids. As 
spring advances, the thickening takes place under the influences of 
heat and moisture. Now we have the conditions of strong endos- 
mosis. Development takes place, next comes evaporation, and 
capillarity acts. These two forces are therefore brought into full 
play, and the whole cellular chain is put into action from root to bud. 
In monocotyledons the upward course is through the most newly 
formed tissues, which are in the interior of the stem. In dicotyle- 
dons it passes along the last formed tissues of the wood, forming a 
pabulum for the cambium. All young tissues are permeable to the 
absorbed fluid, and whatever is formed of a soluble nature in one 
part of the plant, is conveyable to another. Thus a compound 
formed in the leaf may find its way to the stem and even the roots, 
which latter is most likely to take place in the autumn, and indeed 
goes to explain what is called root-action at that season. 
4. The last point was the diffusion of the sap. This subject is at 
present by no means in a settled condition by reason of differences 
of opinion, and the influence which the long received views of a 
regular descent of sap, after elaboration in the leaves, still has upon 
many persons. There is, however, no proof whatever of the forma- 
tion of ligneous tissues in the leaves, and the old theories of Du- 
hamel and others are not to be maintained. Still it is not to be for- 
gotten that it has already been shewn that compounds formed in the 
leaves may pass downwards, therefore the possibility of a descending 
sap remains, while there is no general demonstration of the fact. 
Ascent and diffusion may be regarded as sufficient to account for all 
the phenomena of growth. The old arguments in favour of a 
descending liber current in exogens, such as ringing the bark and 
grafting, are capable of other interpretations than those which they 
have received. A remarkable specimen of stock and graft was 
shewn, to prove that their growths were perfectly distinct, though 
nourished by a common food. If there were a descending bark sap, 
could this be so? The fact is, the new annual rings are formed 
out of a cell development of the cambium. To shew that the proper 
expression for the distribution of the sap is diffusion, an account was 
given, and drawings shewn, of some very remarkable experiments on 
a horse-chesnut, at Glassnevin near Dublin. They tended to prove 
that when the sap-flow from cell to cell was interrupted by the al- 
