Ilex Aquifolium , Z., in Reference to Specific Conductivity. 549 
The actual figures obtained for the C curve are higher for rhodo- 
dendron than for holly, ash, or hazel : thus we have 
Rhododendron 
Holly . 
Hazel . 
Ash 
T 4*5 to 29.9% 
5.0 „ 10.6% 
3-2 „ 20-2 % 
J - 6 .» 9 * 5 % 
Professor Farmer’s figures for the specific conductivity as determined 
experimentally are as follows : 
Rhododendron (A i to E6) . 
ir. 9 ,, 2 r*S % 
Holly 
7 *° » n- 0 % 
Hazel . . 
22.0 „ 40.0% 
Ash . . . . 
4.0 „ 24.0% 
There seems a certain difficulty in correlating these two sets of figures. 
The relation between holly and rhododendron is clear enough, and also that 
between hazel and ash, but when we come to compare the evergreens with 
the deciduous trees there is no similar relation holding, In rhododendron 
there is a higher percentage of the wood occupied by water-conducting 
elements than there is in the hazel, but the hazel shows the higher figures 
for water-conduction as carried out experimentally. The explanation of 
the anomaly may partially be found in the lengths of the continuous vessels, 
in the lengths of the vessel-segments, and in the type of perforation which 
renders the segments continuous. The very considerable variation in the 
lengths of the vessels (5-16 cm.) in rhododendron is to be correlated with 
the great variation in specific conductivity: short vessels with numerous 
unperforated cross-walls increase the resistance to the passage of water; 
similarly, short segments and small scalariform pores increase resistance and 
decrease conductivity. Similar considerations hold good for the conducting 
tissue of the holly. 
In comparing the relative average cross-areas of the vessels in the 
four types of wood examined, we have the following data : 
Rhododendron 
Holly . 
Hazel . 
Ash . 
298 sq. /x— 98 sq. / jl \ 
2 qo „ -52 f Calculated from figures 
422 „ -18 „ [ for average diameters. 
607 „ - 7 » J 
Thus the vessels in the stool shoots of the deciduous ash and hazel 
have on the whole a much larger average cross-area than those of the 
evergreen rhododendron and holly: this accounts in a small degree for 
the high conductivity of the hazel and its relatively low percentage figures, 
because friction and resistance are less in wide vessels than in those with 
small iumina. Similarly, the high percentage figures in the rhododendron 
are partially explained by the smaller Iumina of the individual vessels. 
