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In addition to thus protecting themselves against excessive trans- 
piration, plants inhabiting dry regions have generally a very well 
developed root system, the roots sinking into the soil to a great depth 
in search of moisture : they also exhibit various other modifications 
in their structure. Perhaps the most important of these modifica- 
tions, is the development of water storing ceils, which have the 
power of storing up water when the supply is temporarily increased, 
and yielding it up to the growing ussue when the supply from other 
sources falls short of the demand made upon it by the plant The 
leaves ot Agaves Fourcroyas and Sansevierias ; the stems of Cacti 
and the pseudobulbs of epiphytic orchids, are chiefly made up of 
this aqueous tissue ; the cells of which being gorged with water, 
constitute a reservoir from which the loss of water due to transpira- 
tion is made good. Owing to the presence of this water storing 
tissue, these plants can withstand long periods of drought .without 
injury , he cut branches of Cacti for example, will remain alive for 
weeks or months, even when exposed to the sun, before the stored 
up water becomes exhausted. 
A familiar example of a plant with water storage tissue, occurs in 
the case of th e Purslane {“Gelang Pasir”), an exceedingly commo 
although harmless, 'weed on most estates, especially in the neighbour- 
hood of cooly lines. It has small fleshy leaves which are used as a 
vegetabie by the coolies, and bears little yellow flowers. The 
difficulty of eradicating this plant is known only too well to all 
ers ,’ as ' thinks t° its special provision of water, each small piece 
ot the plant allowed to remain on the ground after hoeing out the 
weeds, is generally able to re-establish itself before becoming 
emcca e .in fact, cultivation of the soil rather assists in spreading 
the plant than otherwise 
As a rule, when the leaf surface is much reduced, the plant is 
armed with thorns: the terrible spines developed on Cacti and other 
xe? ophilous plants, serve as a protection against the depredations of 
herbivorous animals. 
Xerophilous plants are of course most perfectly developed in hot 
deserts as for instance in parts of the United States, Mexico, the 
v ahara and parts of Australia ; but also occur in the \rtic regions 
(where absorption is limited by the prevailing low temperature) and in 
salt marshes, it may seem strange that the plants which form the man- 
grove swamps at the mouths of rivers, and on the sea shore, where 
there is an unlimited supply of water, should exhibit the same struc- 
tural peculiarities as xerophilous or dry region plants: yet an 
examination of their organs show that they too^^ve developed thick 
eaves, sometimes covered with hairs, are provided with water stor- 
ing tissue, and in many respects agree with true xerophytes. The 
explanation of this is doubtless to be found in the fact that such 
plants hnd a difficulty in separating the water from the salt solu- 
tion, and if free transpiration occurred, it would result in an ac- 
cumulation of salt within the tissues of the plant which would prove 
injurious. A similar structure is characteristic of the plants in- 
habiting peat bogs, where the presence of large quantities of humous 
