382 
Certain number of facts and observations which may direct experi- 
menters in their researches. 
In the case for example of Landolphia Heudelotii Dec. which 
supplies the greater part of the caoutchouc exported from Senegal, 
the Soudan and of Guinea it is easy to see in a transverse section 
of the vine that the laticiferous vessels are chiefly found in the 
inner half of the bark but that they are nearly completely absent 
from the centre part of the bark as well as in the zone nearest the 
wood. To get at these vessejs therefore it is not necessary to pe- 
netrate as far as the wood. The vessels in Landolphia Heudelotii 
Dec. are elongate tubes branched and anastomosing with a dia- 
meter varying from 30 to 40 thousandths of a millimeter. They 
extend chiefly in the direction of the length of the stem but as 1 
have just said, branch and these branches run more or less obli- 
quely. 
A transverse section therefore of the bark of a given length and 
depth will cut across a certain number of the vessels from which 
the latex will escape while a longitudinal section of equal length 
and depth will only cut through a much smaller number (a figure 
to shew this is given in the text which we are unable to reproduce 
but the description is intelligible without this. Ed.) It is however 
easy to show this at least in Landolphia Heudelotii in the fol- 
lowing manner. One knows, (and this is what the extraction of 
rubber from the dry bark is based on) that in this vine the latex 
dries of itself in the laticiferous vessels of the bark so that each 
vessel contains a very thin strand of rubber. If then one breaks 
transversely a piece of dry bark and carefully separates the frag- 
ments, one sees them joined by the thin filaments of rubber 
representing the number of vessels in the section. If the bark 
is broken longitudinally (/ e. parallel to the direction of the stem) the 
number of threads of rubber drawn out is very much less, showing 
that the number of vessels cut across by a transverse section is far 
greater than those cut across by a longitudinal section. I have 
besides verified the fact in a young Castilloa, and Willes (Morris 
Cantor Lecture published by the Society of Arts April 1899,) has 
shown that in Heveas cultivated in the gardens at Heneratgoda, 
Ceylon, other things being equal incisions made obliquely at an 
angle of 45 degrees produce twice as much latex as vertical ones. 
Transverse sections offer another advantage in the matter of 
collecting the latex. On account of the constant growth of the 
woody cylinder surrounded by bark, the bark not following this 
growth is stretched more and more, like a too tight coat round a 
stout body. It is this tension of the bark which produces the 
longitudinal cracks so characteristic of the oak of our country for 
example. If one takes off a transverse band of bark from the 
trunk of a tree and tries afterwards to put it back in the same 
place it was taken from it will be found that the ends will no long- 
er meet. 
It is just this tension which causes the escape of the latex which 
without this, capillarity would keep in the laticiferous vessels. 
Now in making a transverse cut one does not reduce the tension 
