Latex and its Functions . 
213 
to depend largely upon the available moisture in the soil. 
After heavy rain the exudation of latex is much more copious 
and thinner, looking as if the vessels had become surcharged 
with water. 
As the necessity for a reserve of water increased, the 
laticiferous system would tend to become more extensive 
and more intimately associated with the surrounding tissues. 
The genus Euphorbia chiefly inhabits dry regions and is one 
of the richest in latex. 
This view does not explain the proteid or starch grains of 
latex, yet, I think, it is one to be borne in mind in studying 
the role of latex in plants, and hitherto it has in the main 
been disregarded. If latex does serve as a water reserve, 
then perhaps it is chiefly valuable for the growing organs. 
Our knowledge of the function of latex can hardly be 
regarded as having advanced as yet much beyond the domain 
of hypothesis. There is a considerable amount of work to be 
done before we can arrive at the true meaning of such a richly 
developed system of milk-tubes as that in an Euphorbia. We 
know very little about the metabolic processes which result 
in the production of the secretions—tannin, resin, caoutchouc. 
We are still very ignorant of the way in which the sieve- 
tubes with their companion cells deal with proteids, though 
it has been suggested that the laticiferous tubes might relieve 
them of part of their work. 
The problem is one of much interest in physiological 
botany, and not without its direct practical bearing on the 
production of the commercial articles, indiarubber and gutta¬ 
percha. The solution of it may show that latex does not 
play such important parts in the plant’s economy as has been 
claimed for it in the past. 
