2 
JOTJENAL OF THE EOYAL HOETICULTUEAL SOCIETY. 
concurrent influences. In its course it is like a great river, which, 
while steadily flowing to the sea, turns to the right or left as 
channels open for it until it reaches the delta near the termination 
of its course, which may be compared to the arrival of the sap at 
the leaves, when it flows in any direction, now dividing to the 
right and to the left, and again even regurgitating and flowing in a 
backward direction, but all these anastomosing together, and ending 
by emptying into the ocean, which for the sap is the atmosphere, 
into which its watery portion is drawn by evaporation from the 
surface of the leaves. 
It is ten years since the paper by Mr. Herbert Spencer to 
which I refer, on circulation and formation of wood in plants (Lin- 
nean Society’s Transactions, vol. xxv.), proved to demonstration 
that the sap ascended in the branches, and that while of course 
he could not prove a negative he at least showed that in none of 
his experiments could he get the sap to descend ; he moreover gave 
a simple explanation of the deposit of wood by the sap oozing 
through the vessels on its way up, and depositing woody fibre 
around them, A few years later Professor "W. R. MeHab repeated 
and extended Mr. Herbert Spencer’s experiments, with the same 
results, and showed that the sap ascended both by the vessels 
appropriated to its ascent, and by those supposed to be appropriated 
to its descent. 
The grounds on which the descent of the sap has maintained 
its place in the belief of men are of three kinds, viz.: Inferences 
from, 1., Practical Horticultural Experiments; 2. from Physio¬ 
logical Experiments ; and 3. from Chemical Experiments. 
As to the first, the experiments seem to me when properly 
interpreted to be wholly opposed to the theory in whose favour they 
are cited. The growth of a callus on the upper side of a cut has 
been cited as one proof, but if it is tested it will be seen that while 
the lower side of the cut is rapidly covered over, that on the upper 
side takes years, and, what is more to the purpose, the callus 
grows almost entirely from the sides. Then a very favourite 
argument, which is usually supposed to be a knock-down 
blow, is, that if we tie a ligature round a branch, the branch 
swells above it as well as below it, but much more above than 
below, and it is said that this shows that there is a descending 
current which the ligature keeps back like a dam. Put it is 
only a misapprehension of the phenomenon to liken it to a dam 
keeping back a descending stream. It is the case of a stream ex¬ 
panding itself when it finds space after its passage through a narrow 
