Hazel-wood zvith Reference to Conductivity of Water . 565 
a rapid falling off in the proportion of mechanical elements differentiated, 
and it may be connected with the smaller size and weight of the leaves borne 
upon this part of the shoot. 
Curve E represents the average diameter of the cavities of the water¬ 
conducting elements present in the wood at different levels in the shoot. 
The range of the actual diameters measured was from 2to 48 ju, ; and the 
highest average figure obtained was 23*27^. On the whole there is a 
Fig. 9. 
general decrease in the size of the vessels from base to apex, but towards 
the base the proportion of tracheides increases, and, as these are of small 
diameter, they tend to reduce the average. This is the case especially 
in the large sections in H7, in which the proportion of tracheides is 
particularly high* The curve keeps fairly level for the lower part of the 
shoot, and then falls, gradually.at first, and more rapidly near the apex. It 
will be seen that the first bend downwards occurs at the region in the stem 
