SUCCULENTS 197 



from a soil saturated with sea-water is characteristic of 

 such plants. When this is so there can be no difficulty in 

 obtaining the necessary supply. Schimper held, however, 

 that reduction in transpiration in such plants would reduce 

 the amount of toxic salt absorbed. Ruhland (1915) has 

 shown that in the Statices and Armerias the root cells are 

 highly impermeable to salts, while the glands with which 

 the leaves are provided excrete the surplus. Furthermore, 

 these plants seem to transpire as rapidly in saline as in 

 ordinary soil. Yet Armeria from an inland station placed 

 in saline solution, though it too excretes salt rapidly, soon 

 shows signs of poisoning. This points to the presence of 

 a constitutional difference between the coastal and the 

 inland varieties — a difference unconnected with the water 

 relations. 



Delf (191 1, 1912) has shown that, while the salt suc- 

 culents are xerophytic in so far as they store water, and in 

 many cases possess thickened cuticle, waxy bloom, and 

 protected stomata, they do not withstand drought like the 

 desert succulents, but flag and wither very rapidly. The 

 question is still further complicated by the fact that suc- 

 culence is not confined to the plants of the salt marsh, but 

 is shown, often markedly, by those inhabiting dunes or 

 rocks near the sea, e.g. by Arenaria peploides, Cochlearia 

 officinalis, and Plantago maritima. The salt content of 

 the soil of these stations must be relatively very low, 

 though higher than inland. The succulents of saline and 

 alkaline soils inland, where salinity is combined with a 

 desert climate, are subject to entirely different conditions. 



The desert succulent is a plant with a large water balance, 

 reduced surface, and low transpiration, features clearly 

 related to the conditions in which it grows ; but it is evident 

 that the apparently xerophytic characters of the salt succulent 

 cannot be so easily related to their environment. 



Recently MacDougal, Richards, and Spoehr (1919) have 

 offered a suggestion as to the causation of succulence. Their 

 work is based on comparison of thin-leaved and fleshy- 

 leaved specimens of Castilleja latifolia, of the same genetic 



