202 THE COAST-FLORA OF THE CLACTON DISTRICT. 
with different places, but that in the same place it is by no means 
stationary. 
Most plants growing in the salt-area show definite alterations 
in their tissues, notably succulence, which may be either of the 
leaves or of the stem. Succulence must be regarded as a sign 
of lack of water : the saline soil, even when wet physically, is 
physiologically dry. The plants cannot absorb the sea-water 
plentifully, because they have no machinery to get rid of the 
salt, which has once entered their tissues, and must, therefore, 
render transpiration as slow as possible, which is precisely the 
case of xerophytism. This is the usual explanation of succulence : 
Halophytes are a type of Xerophytes. Against it it may be 
said that the Halophytes have neither fewer stomata than other 
plants, nor are those in any way protected. Diels asserted that 
succulence was a means by which the plant freed itself from an 
excess of salt ; he held that, favoured by the frequently red- 
coloured cell-sap, certain organic acids were formed in the tissues 
which entered into volatile compounds with the chlorine. His. 
analyses seemed to show that, when supplied with pure water 
only, a diminution of chlorine in the leaves actually occurred, no 
trace of salt being found in the water itself. However, later 
research appears to have disproved Diels’ theory. What happens 
is that the plant withdraws the salt from the actively growing 
shoots and stores it up in the older leaves and in the stem. 
Lesage made a series of very interesting culture experiments 
which established that increase in salt tended (i) to promote 
succulence (the palisade cell-layer becomes thicker, salt acting 
morphologically like sunlight), (2) to diminish the amount of 
chlorophyll (which accounts for the translucence of the leaves), 
(3) to decrease the size of the leaves, and (4) to dwarf the size 
of the whole plant. Reversing the argument, the degree of 
succulence, etc., may be said to be a good test of the degree of 
salinity of the soil. 
The question whether the physical or chemical nature of the 
soil, including moisture, is of primary importance to the plant 
is the subject of a long-standing controversy among botanists. 
In the psammophilous shore vegetation, the physical properties 
of dryness, and looseness of particles, evidently co-operate with 
the chemical action of the salt and the poverty of nutritive 
substances in producing an extremely xerophytic vegetation. 
