CRAIB—REGIONAL SPREAD OF MOISTURE INWoop OF TREES. 7 
tests showing the distribution of the tanrin served to confirm the 
supposition that this white zone is sap-wood in process of 
conversion into heart-wood by the extraction of moisture of 
imbibition followed by impregnation of the walls with tannin. 
Further, microscopic sections showed that the tannin is 
actually in the walls of the tracheids, that there is no trace of 
tannin in the medullary ray cells and that the medullary ray 
cells are living in the white band. ‘Thus a means of communica- 
tion is still open through the medullary rays from sap-wood to 
heart-wood even supposing the impregnation of the tracheid walls 
with tannin were to act as resin in preventing diffusion through 
the walls. 
Plate CLXXXIX gives the moisture distribution in Taxus 
baccata in November, showing the high moisture-percentage of 
the sap-wood, the sudden dip owing to the low moisture- 
percentage of the white band and the rise in percentage on 
entering the heart-wood. 
The coloured plate (CLXXXI) is a reproduction of a painting 
made from the newly felled wood of this tree to show the 
conspicuous white band separating the heart-wood and sap-wood. 
V. Wind as an Agent in Moisture-Spread (Plate CXC). 
That wind is a very effective agent in the raising of the sap in 
trees is a well-known fact but in the accompanying graph the 
results of a gale are shown to be not only sap-raising ; there is 
in addition a disturbing of the sap-distribution equilibrium. 
The tree examined was a specimen of Populus trichocarpa 
which was blown down during a severe gale on the early morning 
of 1st March 1918. The results probably do not give the 
maximum effects of the gale as, not suspecting any such disturb- 
ance of the moisture distribution, I treated the tree in an exactly 
similar way to that adopted for the other trees examined, i.e. by 
determining the moisture-distribution in strips from north to 
south and east to west through the centre. Fortunately, however, 
the gale was from only slightly east of north so that the maximum 
results shown in the graph are those from north to south 
Without attempting a physical explanation of the results I 
would simply draw attention to the increasing percentage in the 
youngest wood as we ascend the tree on the side on which the gale 
was blowing, to the decreasing percentage in the youngest wood 
on the side away from the gale, and to the great contrast in the 
percentages of these two sides. 
It must be borne in mind that in such a tree as Populus tricho- 
carpa with its elasticity -we would find a maximum moisture dis- 
turbance. In less flexible trees such as Quercus or Platanus the | - 
j result of a gale would probably be very much smaller. 
