HALOPHYTES 169 
phytic during that season. Evergreens of cold climates, e.g. 
the pines, have xerophytic leaves. 
Further details will be found in Part II. ; see the orders 
and genera mentioned above, and Velloziaceae, Cheilanthes, 
Espeletia, Dasylirion, Lewisia, &c. 
Sea-coast and Salt-steppe Plants, or halophytes \ 
exhibit xerophytic characters, but form so distinct a group 
that it is convenient to deal with them separately. The 
presence of salt renders absorption of water by the roots 
slow, and thus there is less available for transpiration, and 
at the same time its presence in the assimilating cells checks 
the process of assimilation and may even stop it altogether 
or kill the plant if the concentration become too great. A 
reduction of transpiration is a primary necessity to such 
plants. There are also many plants that grow on sand-dunes 
a little way from the sea ; here there is less salt but the soil is 
not retentive of water, and therefore there must be a reduc- 
tion of transpiration. The group is composed of members 
of many natural orders, e.g. Chenopodiaceae, Aizoaceae, 
Plumbaginaceae. The Rhizophoraceae, Frankeniaceae, &c., 
consist chiefly of halophytes. 
The structural characters of halophytes are described 
below in dealing with the zones of vegetation. They show 
in general a marked xerophytic structure, with a decided 
tendency to succulence. Many have fruits or seeds specially 
adapted to transport by marine currents. 
Mesophytes 2 . Under this term Warming classes plants 
occupying, in regard to dryness of the soil and air in which 
they live, an intermediate position between hydrophytes and 
xerophytes. They live chiefly in districts where the rainfall is 
pretty evenly distributed through the year, e.g. in the colder 
parts of the temperate zones, and in the equatorial regions. 
They form meadows, evergreen or deciduous woods, coppices, 
&c. Usually there are many species, and they cover the 
ground very fully. Evidently the group shades into the 
xerophytes, including a large part of the tropophytes above 
mentioned. 
1 Warming, Halofytstudier in ICgl. Dansk. Vid. Selsk. Skr. 6, vm. 
1897 ; Oekologische Pflanzengeographie {cf. literature there quoted) ; 
Schimper, Die Indovialayische Strandflora, Jena, 1890. 
2 Warming and Schimper, op. cit. 
