Delf. — - Transpiration in Succulent Plants . 413 
cuticularized than that of the same species living on the plains ; and here 
again the function of the cuticle appears to be primarily protective rather 
than mechanical, as Fleischer 1 believed. Wiegand 2 suggests that cuti- 
cularization is particularly characteristic of plants which are exposed at all 
times to the danger of too great transpiration ; whereas a thinner cuticle 
with a covering of hairs is more often found in plants in which transpiration 
must be reduced at times, and yet must remain unhindered when the air is 
damp, and transpiration therefore rendered difficult. 
Schimper claimed that a thickened cuticle, as well as other xerophilous 
adaptations, is to be found in most epiphytes , 3 in Mangrove plants , 4 and in 
the plants of the Solfataras , 5 or regions bordering a fumarole. He stated 
that in the first case the precarious water supply rendered protection against 
too rapid evaporation necessary ; in the second case the presence of chlorides, 
and in the third case of sulphates in the soil, renders the process of absorp- 
tion so difficult that the transpiration also must be diminished by means of 
xerophilous adaptations. According to the more recent observations of 
Holtermann , 6 however, this is by no means always the case. The epiphytic 
vegetation was found to occur, at least in Ceylon, mostly in damp tropical 
or subtropical forests ; the plants found in such localities showed little or no 
cuticularization of the epidermis, and they were, as a matter of fact, found 
to be capable of very rapid transpiration ; such are, for example, many 
species of Ficus , Peperomia , Drymoglossum , many Bromeliaceae, and some 
Orchidaceae. A few epiphytic orchids which were found growing in a dry 
atmosphere had a thickened cuticle, but these were distinctly exceptional. 
In Sonneratia , Rhizophora , and other plants of the Mangrove formations 
there was similarly but little development of cuticle, and, at times, a rapid 
rate of transpiration. In Agapetes vulgaris and Rhododendron retusum , 
the two most characteristic plants of the Solfataras of Ceylon, there was 
also absolutely no protection against excessive water loss. 
Aubert 7 measured the rate of transpiration of a number of succulent 
and mesophytic plants and came to the following general conclusions : 
1. With equal surfaces, succulent plants, such as many Crassulaceae 
and species of Mesembryan themum which have a thin cuticle, transpire 
more freely than many mesophytes with a thick cuticle ( Hedera Helix, 
Picea excelsa ) ; with equal fresh weights, however, the succulent types 
transpire less than these. 
1 Quoted by Dr. A. Burgerstein, loc. cit., p. 205. 
2 Wiegand : Relations of Hairy and Cutinised Coverings to Transpiration. Bot. Gaz., 1910, 
3 Schimper, A. F. W. : Die epiphytische Vegetation Amerikas, 1888. 
4 Schimper, A. F. W. : Die indomalayische Strand-Flora, 1891. 
5 Schimper, A. F. W. : Ueber Schutzmittel des Laubes gegen Transpiration, besonders in der 
Flora Javas, 1890. 
6 Holtermann, Dr. C. : Der Einfluss des Klimas auf den Bau der Pflanzengewebe, 1907, 
pp. 138, 61, 73. 
7 Aubert, E. : Turgescence et transpiration des plantes grasses. Ann. des Sci. Nat., Bot., 1892. 
