CRAIB—REGIONAL SPREAD OF MOISTURE IN Woop OF TREES. 189 
and comparison of the conditions found in the stock and in 
the scion. As a preliminary it will be well to give a fuller 
description of the plate. 
As already stated, the stock was probably Pyrus Aria, and 
the scion was a form of that species. The tree was felled entire 
on the morning of oth April 1919, at which time the buds were 
considerably swollen, though none were yet open. The spread 
of the moisture radially away from the centre has made con- 
siderable progress, the stage reached in this movement being, 
as noted above, practically that of the March Acer. 
The line of the graft is shown very clearly marking off 
the stock and the scion as two regions whose physiological 
activities, at least as regards moisture-spread, do not synchronise, 
The stock is visibly ahead of that part of the scion immediately 
above it in the extent to which the radial spread of the moisture 
has been carried. As a natural consequence of the more 
advanced stage reached by the stock, we find that a wet part 
ot the scion overlies a dry part of the stock. Without some 
restraining influence, we should naturally expect the moisture 
from the wetter region to diffuse downwards along the walls of 
the drier cells immediately below. 
Cannot one deduce from this that the moisture-spread is a 
controlled or vital phenomenon and not a purely physical one ? 
To all intents and purposes a grafted tree of this age is structur- 
ally one tree, and if the moisture-spread were a purely physical 
happening then there would not be such a marked and sudden 
difference in the amount of the spread above and below the 
graft-line. Both stock and scion perform their accustomed 
cycles independently. This touches many important biological 
problems, the consideration of which must be dealt with in 
subsequent papers. 
