428 Delf.— Transpiration in Succulent Plants . 
and others) were grown in ordinary soil in the Botanic Gardens at Peradenyia, 
but were watered with salt solutions of varying strength. After a time the 
culture plants were compared with the same plants growing in their natural 
habitat. In nearly every case the aqueous tissue was found to be less 
developed than the normal in those plants which had been watered with 
dilute solutions, and it was more strongly developed in those which had 
been watered with more concentrated solutions of salts. In one instance 
the leaves of a swamp plant of Avicennia officinalis had from four to five 
layers of aqueous tissue, whereas leaves from a plant cultivated at Peradenyia 
and watered with a 5 per cent, solution of potassium chloride showed from 
seven to eight layers. In the case of the flora of the Solfataras, observed 
by both Schimper and Holtermann, the excessive amount of sulphates in 
the soil appears to have the same effect in favouring the formation of 
aqueous tissue as the chlorides in the case of the Mangrove vegetation. 
Not only are succulent plants provided with a reserve of water, but 
very often there is a marked conservation of the water supply, the younger 
leaves in time of drought being kept continually turgid at the expense of 
the older ; this is probably true of all succulents with the exception of those 
which, like Salicornia , live in very moist habitats. It is also true, although 
to a much less extent, of a large number of mesophytic plants. 
Meschayeff, in 1882, appears to have been the first to call attention to 
the oecological importance of this movement of water in plants ; and sub- 
sequently numerous other observations of the same kind were made. 
Haberlandt hung up cut shoots of Rhizophora mucronata without any water 
supply. After one day the older and yellower leaves became withered, 
while the remaining leaves, except the youngest, were scarcely withered. 
A more careful experiment is that of Burgerstein, who chose a pot 
plant of Gasteria vittata y a plant which has opposite pairs of fleshy leaves. 
The pot was allowed to stand with no water in a sunny place for six weeks, 
at the end of which time the earth was quite dry. Six leaves on one side 
were now cut off and weighed, the water content of each being found 
separately. The plant was now well watered, so that at the end of a month 
all the leaves seemed to have recovered their turgidity. The six remaining 
leaves were then detached and weighed, their water content being calculated 
as before. In comparing the water content of the full and the nearly 
depleted leaves, the amount of depletion was greatest at the lowest leaf and 
fell off regularly to the uppermost, as may be seen from the figures in 
Table VI. 
The same gradual depletion of the old leaves at the expense of the 
young may be demonstrated more simply by observing the shrinkage in 
the dimensions of the different leaves on a shoot when allowed to wither. 
I have made such observations with species of Mesembryanthemum and 
of Seduni. 
