Delf. — Transpiration in Succulent Plants . 437 
in many succulent desert types, and during the periods of rapid transpira- 
tion the aqueous tissue may become so depleted of its water that the leaf 
becomes perceptibly flaccid. This, indeed, frequently happens after a hot 
day, according to Holtermann, in the plants of the Mangrove swamps. 
The following morning, however, the leaves may be found erect and turgid 
again after a night of heavy dew, so that Holtermann suggests that an 
appreciable surface absorption of the dew must have taken place. On the 
other hand, it is possible, in the light of the experimental researches of 
Wiile 1 and others, that root absorption persisting all through the hours of 
suspended transpiration would alone account for the change. A similar 
phenomenon may easily be seen in our British halophytes, and probably 
the same explanation may be found true. 
The experiments of Haberlandt and Holtermann on Mangrove plants 
indicate that here, as in true xerophytes, there is some power of water dis- 
placement, but to a somewhat less extent than in typical desert and rock 
plants. I have noticed a distinct power of water displacement from old to 
young leaves during withering, in shoots of Salsola Kali and in Mesembry- 
anthemum edule , and to a less extent in Snaeda maritima \ the same power 
may exist in Salicornia , but if so it is not sufficient to prevent the young 
parts from withering in drought, before the older internodes appear to 
suffer. The displacement of water from old to younger parts in time 
of need is by no means limited to succulent plants ; it is often to be seen 
in mesophytes, although here it is less obvious, and probably of little 
biological importance. 
In the majority of halophilous and in many epiphytic plants, the 
transpiring surface is little protected from water loss, being usually glabrous, 
with little cuticle or none, and with often numerous unsunken active stomata ; 
relative to the surface area the transpiration may often be far greater than 
obtains in the majority of mesophytes under the same conditions. 
The question of the relation of the halophytic plant to its environment 
is one of much difficulty. There is no doubt, as Schimper, Lesage, Holter- 
mann, and others have shown, that it is intimately related to the presence 
of chlorides in the habitat. Probably the conclusion of Warming comes 
nearest the truth : that, whereas some maritime plants are true halophytes 
and cannot thrive in the absence of chlorides, others are only halophilous 
and, whilst showing greater succulence in the presence of chlorides, can 
thrive almost equally well in their absence ; such are Aster Tripolium and 
Plantago mai'itima , and numerous other examples might be given. More- 
over, owing to concentration by atmospheric evaporation and to dilution by 
rainfall, the salt content of the soil water must always be a very variable 
factor, and the halophyte must, therefore, possess in an unusual degree the 
power of accommodation to such changes. Further evidence on this 
1 Quoted by Burgerstein, loc. cit. 
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