ECOLOGICAL CLASSIFICATION OF PLANTS 13 
Mesophytes differ from Hydrophytes in having a well- 
developed wood system for the conduction of water and food 
material, as well as for other purposes. In Water-Plants there 
is no current of water through the plant as in Mesophytes, for 
‘plants living in water imbibe their nourishment along their 
whole surface, and it passes from cell to cell by a process of 
‘diffusion; in Mesophytes a conducting tissue, such as wood, 
is necessary for the conduction of water and substances 
dissolved in it. 
The root, stem and leaf of Mesophytes show a considerable 
variety of structure according to the habitat of the plant. 
These will be fully discussed in Part II.; here the following 
groups, which have peculiarities in their mode of life, and 
which occur in varying habitats, are considered—namely, 
(a) Climbing Plants ; (>) Insectivorous Plants ; (c) Parasitic 
and Saprophytic Plants. we 
(w) Climbing Climbing Plants are subdivided by Darwin into : 
Plants. (j.) Twining Plants ; (1i.) Climbers with sensitive 
organs ; (ii.) Hook Climbers; (iv.) Root Climbers. Honey- 
suckle, and Woody Nightshade, may be taken as instances of 
woody plants which climb by means of entwining their stems 
over bushes and trees to a considerable extent ; their stems 
increase in thickness from year to year. Hop, Convolvulus, 
Black Bryony, also climb by means of twining stems, but 
these come up fresh each year from the rhizome ; the Scarlet- 
Runner is an example of an annual with a twining stem. — 
The tip of the stem in twining may describe quite a large 
circle, and thus has a good chance of finding support. The 
spiral may be in the direction of the hands of a clock, or 
in the opposite direction; usually the same species twines 
the same way throughout. The Nasturtium and Clematis 
are instances of plants that climb by twining petioles. 
Climbers with sensitive organs for the most part develop 
tendrils, which may be stems, leaves, or parts of leaves. 
Stems modified into tendrils occur in the Virginian Creeper 
and in the Grape-vine. The tendrils, by means of which the 
Passion-flower climbs, are also modified branches. 
