188 CRAIB—REGIONAL SPREAD OF MOISTURE IN Woop OF TREES. 
the annual ring as the unit structure of the wood. The 
necessary cutting of the wood into absolutely equal sections 
would result in many, if not all, of these sections having a 
disproportionate amount of either spring or summer wood. If 
the true balance between the two regions of the annual zone 
be not preserved, then, as has been proved experimentally, 
distorted results will follow.. There is -another objection. 
Uniformity in the wood would be postulated, e.g. an occluded 
dead branch would vitiate the whole results, or, if the branch 
were cut out, allowance could only be made by accurate volu- 
metric determination. 
As confirming the results arrived at by the methods adopted 
by me, we find that newly felled timber, especially when seen in 
median longitudinal section, gives a visible demonstration of the 
distribution of the moisture. An approximate graphic repre- 
sentation of the moisture-distribution can be made from a glance 
at the newly felled wood. This statement is made on the 
strength of results of trials during the experiments. On several 
occasions I constructed graphs of the moisture-distribution from 
the appearance of the wood in longitudinal section, and these 
graphs agreed in their main details with the graphs made from 
the calculations following on the drying of the sections. 
That the main details of the moisture-distribution can be 
gauged from visual examination can be confirmed, I think, by 
reference to the accompanying plate, which is a reproduction 
of a photograph through the graft-region of a newly felled tree 
of which the scion was a form of Pyrus Aria and the stock was 
probably Pyrus Aria. 
Excluding the dark-coloured heartwood, which occurs only 
in the stock, we find that both stock and scion have a central 
pale-coloured area bounded on both sides by darker-coloured 
areas. The colour-shades are due to the moisture-content, the 
darker-coloured areas having a much higher moisture-content 
than the paler-coloured, and the transition between the two areas 
is not abrupt but gradual. A graph constructed from these 
details would be low in the central region, rising with some 
irregularities through the intermediate region to its maximum 
in the youngest wood. This brief general description would 
apply to the graph of the lower parts of the trunk of Acer 
Pseudoplatanus for March* if we leave out the very dry 
youngest wood of the Acer. And with the same proviso the 
two finished graphs correspond in their general outline. 
So far I have referred to the accompanying plate as a visible 
demonstration of moisture-distribution in wood. Of much more 
interest are the deductions to be drawn from an examination 
* Craib in Notes Roy. Bot. Gard. Edin., xi, pl. clix (1919). 
