212 
Parkin.—Observa tions on 
being channels for the transport of these materials is one 
which has received much consideration. The early develop¬ 
ment of the system in the embryo and young organs, as well 
as its association with the sieve-tubes, are brought forward in 
favour of this theory. It has even been suggested that in 
certain plants they take the place of sieve-tubes, since these 
latter diminish in number as the laticiferous tubes increase. 
Another hypothesis put forward is that latex functions 
as a protection to the plant, either by closing wounds or 
by checking the ravages of insects. No conclusive evidence 
has been brought forward to show the likelihood of the latici¬ 
ferous system of any plant having been evolved for such 
reasons. These plants seem just as liable to insect pests and 
fungus-diseases as others. In a tree like Hevea with thick 
latex, no doubt an injury to the bark is effectually closed 
by a plug of rubber, thus preventing, we may suppose, the 
entrance of fungus-hyphae, but to conclude that the latex has 
been elaborated for such a purpose is another matter. 
If the formation of laticiferous tubes has been called forth 
in all plants possessing them to perform a common function, 
then I am inclined to think the idea of their serving as 
channels for holding water in reserve as one of th^ most 
plausible. Laticiferous plants are markedly characteristic 
of tropical regions, where transpiration is great. The develop¬ 
ment of a system of tubes running throughout the plant to 
be filled with water during the wet season and then to be 
gradually drawn upon during times of drought, is intel¬ 
ligible. 
Warming, in a paper in the Botanical Gazette for January, 
1899, entitled ‘Vegetation of Tropical America,’ mentions 
lianas and other plants of tropical forest and scrub as often 
laticiferous, and says, ‘ most likely latex serves several purposes, 
and one of them, I suppose, is to supply water to the leaves 
in times of need when transpiration becomes too profuse.’ 
From our experiments in Ceylon we found that the quantity 
of latex extractable from incisions in the trunks of Hevea 
trees varied considerably with the time of year, and seemed 
