Delf . — Transpiration in Succulent Plants. 441 
ties observed ; for, although many plants, such as Salicornia , are modified 
so far as to be obligate halophytes, and others, such as Aster Tripolium^ are 
plastic or facultative, yet there are some plants which can endure a saline 
or non-saline habitat with little or no change of structure, such as Suaeda 
fruticosa and several species of A triplex. In every case, however, the 
aqueous tissue appears to be mainly of value as a water-storage tissue, the 
cells of which are always depleted in time of drought before the assimilating 
cells lose in turgidity, and filled again when a renewed water supply is 
available. 
Finally, we see that many of the peculiarities of succulent plants must 
be regarded as adaptations to environment of real importance to the plant. 
They may be produced during the lifetime of the individual, as in the 
development of additional mesophyll or storage tissue in a facultative 
halophyte, or they may appear as permanent characteristics, as in the 
case of plants which are found exclusively in saline situations. In all 
cases, however, the presence of aqueous tissue and the power of water 
storage are probably of the first importance in the economy of the indi- 
vidual, and enable it to support a rate of water loss which is very con- 
siderable, relative to the transpiring surface. 
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