438 Delf. — Transpiration in Succulent Plants. 
point is given by some experiments of Mr. T. G. Hill. 1 Observations 
of the concentration of the soil water of the salt-marsh at Erquy, before 
and after heavy rain, showed a concentration of mixed chlorides varying 
from 3-3 per cent, to 07 per cent. ; there is thus a definite dilution or 
‘ washing out ’ of the salts present in the soil. Measurements of the 
osmotic equivalent of the root-hairs of young plants of Salicornia gave 
an average value equivalent to a 5 per cent, or 6 per cent, solution of 
sodium chloride when these plants had been growing in soil of which 
the soil water contained about 3 per cent, of chlorides. After bathing such 
a sod containing Salicornia seedlings with weaker solutions of chloride 
or with water, the root-hairs were found to have a correspondingly lower 
osmotic pressure ; and, conversely, when seedlings which had acquired 
a lower osmotic pressure were transferred to successively stronger solutions 
and re-examined, the root-hairs were found to have regained a higher 
osmotic equivalent. There is, therefore, a definite accommodation in the 
cell-sap of these root-hairs to solutions of gradually increasing or gradually 
decreasing concentration. It would be of great interest to know how far 
the same property is possessed by ‘ halophilous ’ or facultative halophytes 
like Aster Tripolium or Plant ago maritima, and by mesophytes. 
It has long been known that there are some striking parallelisms 
between the adaptations of some halophytic and alpine plants, especially in 
the more succulent types. Occasionally exactly the same species are found 
on mountain-tops and in maritime districts far from each other, as in 
the case of Dodonea viscosa, which, according to Schimper, occurs in Java 
only in these two positions, and in Plant ago maritima, which occurs in 
Europe, either as an alpine or littoral form. 
Bonnier 2 has made a careful physiological analysis of the conditions 
affecting alpine plants. He found that the strong unshaded light in high 
altitudes was largely responsible for the modifications in structure found ; 
whilst the intense cold and dry or rocky soil produced the well-known 
dwarf habit with long, deeply penetrating root system. The typical alpine 
plant, as well as the typical halophyte, shows much greater fleshiness in the 
assimilating organs, largely due to an increase in the depth of a palisade 
parenchyma ; but in alpine plants this is accompanied by an actual intensi- 
fication of pigmentation, so that there is a more rapid assimilation in alpine 
than in lowland forms, whereas in halophytes the thickening of the leaf 
is connected with feebler development of chlorophyll and less active 
assimilation, many of the internal cells of the mesophyll being probably 
almost entirely given up to the storage of water. In the case of alpine 
plants Bonnier regards the more intense pigmentation as a direct adaptation 
1 Hill, T. G. : Observations on the Osmotic Properties of the Root-hairs of Certain Salt- 
marsh Plants. New Phytologist, 1908. 
2 Bonnier, Gaston : Adaptation des plantes an climat alpin. Ann. des Sc. Nat., Bot., 1894. 
