422 Dclf— Transpiration in Succulent Plants. 
examined next day showed much wrinkling and folding on the outside 
walls of all the cells except the guard cells, which were perfectly turgid, 
although all were closed or only narrowly open ; the leaf itself did not 
appear at all limp to the eye or to have suffered from want of water. The 
whole leaf was then immersed in water, and in less than three hours had 
increased in weight by 13-7 per cent. The epidermis was again examined, 
and the wrinkling of the epidermal cells was much less apparent ; about 
half the cells showed no wrinkling at all, and in the remaining cells the folds 
were clearly less numerous. Here, then, we have a case in which the 
epidermal cells may be partly depleted and filled again, without apparent 
injury, as in true aqueous tissue. 
Glands are not found as a rule on succulent or semi-succulent leaves 
and stems. Volkens, 1 however, records the presence of glands on the 
somewhat fleshy leaves of Cressa ere tic a, Reaumuria hirtella , Tamarix 
manifera , and Frankenia pulverulenta , which appear to excrete salts, chiefly 
sodium chloride ; these salts seem to have the power of condensing 
moisture, even from an apparently dry atmosphere, so that the leaves 
sometimes appear to be covered with moisture when no rain has fallen and, 
all around, the vegetation is dry. There is some difficulty in supposing 
with Volkens that the glandular tissue can so far alter in permeability as to 
first excrete a highly concentrated salt solution, and then absorb only pure 
water back again ; but there appears to be no doubt that the layer of salt 
may be of value in preventing water loss, for these plants are found in some 
of the driest regions of the Egyptian-Arabian desert, and can withstand 
long and severe drought. If, however, the layer of salt be removed from 
the leaves of a cut shoot, the power of resistance to desiccation is strikingly 
diminished. 
According to Rohlf 2 the same function is subserved by the glands in 
the leaves of some desert species of Statice ; and Holtermann observed in 
the leaves of Laguncularia racemosa , Acanthus ilicifolia , and Aegeciras 
racemosa (all Mangrove plants) superficial glands which, when tested with 
thallium sulphate, showed an abundant salt content, and which sometimes 
even showed minute crystals of salt visible to the naked eye. Holtermann 
interprets the function of these glands as excretory, the salt being washed 
away by the dew, which falls heavily in those regions at night. The 
excretion of salt by these glands is used as an argument against Schimper’s 
theory that salt accumulates in the leaves of halophytes to a harmful extent. 
Similar glands are found on the leaves of some European species of Statice , 
Glaux , and other halophytes ; but these are scarcely succulent in habit, and 
little is known of the true function of the glands in these plants. 
It is well known that many plants are capable of absorbing water over 
1 Quoted by Dr. A. Burgerstein : Die Transpiration der Pflanzen, 1907. 
a Quoted by Dr. A. Burgerstein : ibid. 
