Xerophytes.These are plants which live in very dry places, where the substratum has less than 10% of water.
Such terms as hydrophytes, xerophytes, and halophytes had been used by plant geographers before Warmings time e.g., by Schouw;4 and the terms evidently supply a want felt by botanists as they have come into general use.
The criticisms were directed chiefly to the inclusion of sand dune plants among halophytes, to the exclusion of halophytes from xerophytes, to the inclusion of bog xerophytes among hydrophytes, to the inclusion of all conifers among xerophytes and of all deciduous trees among mesophytes, and to the group of mesophytes in general.
Schimper used the term xerophytes to include plants which live in soils which are physiologically dry, and the term hygrophytes those which live in soils which are physiologically wet or damp. Schimper recognized that the two classes are connected by transitional forms, and that it is useless to attempt to give the matter a statistical basis.
It is only in a general sense like Schimpers that such ecological terms as xerophytes have any value; and it is not possible, at least at present, to frame ecological classes, which shall have a high scientific value, on a basis of this nature.
Whilst Schimper objected to the constitution of a special category, such as mesophytes, to include all plants which are neither pronounced xerophytes nor pronounced hygrophytes, he recognized the necessity of a third class in which to place those Schuuw, Grundtraek til en almindelig Plantegeografie (Kjbbenhavn, 1822); German trans., Grundzuge einer allegemeinen Pflanzengeographie (Berlin, I 823).
Xerophytes.Plants which grow in very dry soils; e.g., most hens, Ammophila (Psamma) arenaria, Elymus arenarius, Anasis aretioides, Zilla macro ptera, Sedum acre, Bupleurum spinosum, rtemisia herba-alba, Zollikofferia arborescens.
Hydro-xerophytes (bog xerophytes) .Plants which live in ~t, peaty soils, and which possess aeration channels and xeroiilous leaves; e.g., Cladium Mariscus, Eriophorum angustifohium, if bus Chamaemorus, and Vaccinium Vitis-Idaea.
Tropophytes.Plants which are hygrophytes during some favorl part of the year and xerophytes during the rest of the year; ~., deciduous trees and shrubs, deciduous herbaceous plants with iderground perennating organs, and annuals and ephemerals.
Xerophytes.These plants have devices (a) for procuring water, (b) or for storing water, (c) or for limiting transpiration; and these adaptations are obviously related to the physically or physiologically dry habitats in which the plants live.
The stems of some xerophytes, e.g.
The transpiring surface of xerophytes is frequently reduced.
Many xerophytes are hairy or have sunken stomata which may be further protected by partial plugs of wax:
Bog Xerophytes live in the peaty soil of fens and moors which are physically wet, but which are said to be physiologically dry.
Bog xerophytes), or that the physical drought of summer is unfavourable to shade-loving plants.
For instance, some xerophytes are dry and hard in structure, whilst others are succulent and fleshy.
The effect of external conditions is confined to the modification in various directions of members or organs already existing, and cne very common direction is that of reduction or entire disappearance of parts: for instance, the foliage-leaves of certain xerophytes (e.g.
They are eminently dry-country plants (xerophytes); the narrow leaves are protected from loss of water by a thick cuticle, and have a well-developed sheath which embraces the stem and forms, with the sheaths of the other leaves of the rosette, a basin in which water collects, with fragments of rotting leaves and the like.