ECOLOGY 619 
ples of these plants are the Salt Marsh Samphire, Salicornia 
ambigua, the Mangroves (Rhizophora), the Goosefoots (Cheno- 
podium), and the Bald Cypress (Taxodium). 
XEROPHYTES.—The plants of this group, like the halophytes, 
are adjusted to live in a soil which is physiologically dry. The 
soil may owe this condition to its physical nature, such as porosity 
(sand), or to the presence of humic acids, or by chemical action, 
which inhibits the absorption of water. They are adapted to 
meet the conditions of strongest transpiration and most precarious 
water supply. ‘To meet such conditions of physiological drought, 
the plants show various structural adaptations. In deserts, 
where the atmospheric precipitations are less than a certain 
limit, the plants acquire a xerophytic structure, such as succu- 
lency, water storage tissue, associated frequently with mucilage, 
lignified tissues, thick cuticle to the leaves, depressed stomata 
(frequently in pits), reduced transpiration surfaces and thorns. 
Mechanical tissues like wood and bast fibers attain their highest 
development in these plants. Cacti, conifers, lichens, and the 
century plants (Agave) are types of xerophytes, while many bog 
plants like the cranberry and Labrador tea, with noc leaves, 
are xerophytic. 
MEsopnyTes.—These are plants that grow in soil of an inter-_ 
mediate character which is neither specially acid, cold or saline, 
nor excessively wet or dry, but is sufficiently well supplied with 
water and rich in the elements required for plant growth. 
Plants which grow under such conditions do not have structures 
by which transpiration is closely controlled. They have large 
leaves frequently toothed and incised, with numerous stomata 
__on lower or both surfaces, a thin, moderately cutinized epider- 
mis, and small intercellular-air-spaces. ‘The leaves and stems 
are usually of a fresh green color. ‘Typical of the mesophytes 
are the grasses, the crop plants of field and garden, and most of 
the annual and biennial herbs of temperate regions. 
TROPOPHYTES.—This, term was first introduced by Schimper 
in 1898 for land plants which have deciduous leaves and whose 
conditions of life are, according to the season of the year, alter- 
nately those of mesophytes and xerophytes. The mesophytic 
condition is found in summer, when the trees, shrubs and peren- 
