58 STEMS AND STALKS. 



ness, even for a plant to live without elaborating its own food. 



Parasitic plants are common in tropical regions ; sometimes 

 many kinds are found upon the same tree, presenting a curious 

 variety of foliage. In our climate, except in the Cryptoga- 

 mous family, as lichens, mosses, &c. we have but few genera 

 of these plants.* The Dodder and Misletoe are celebrated 

 parasitic plants. 



Some plants grow without roots; these are called air plants : 

 they are furnished with leaves or stems which seem to inhale, 

 but not to exhale fluids ; their substance is usually fleshy and 

 juicy ; some of them flourish in the most dry and sandy places, 

 exposed to a burning sun ; as the Stapelia, sometimes called 

 the vegetable camel. The Epedendrum grows and blossoms for 

 years, suspended from the ceiling of a room and nourished only 

 by air. 



Many roots, as the rhubarb, wild-turnip, blood-root, &c. 

 possess important medicinal properties. The growth of the 

 root is most rapid in autumn ; at this season, the sun being less 

 powerful and the air more charged with moisture, the juices 

 condense in the lower part of the plant, and nourish it, but as 

 the season becomes cold, vegetation is checked ; the winter is, 

 therefore, the time to collect roots for medicinal purposes. 

 Stems and stalks. 



The trunk or stem is the body of a plant, whether it be a tree 

 like the oak, a shrub like the lilac, or an herb like the pepper- 

 mint or sage ; its use is to sustain the branches, leaves, and 

 flowers ; and it serves as an organ of communication between 

 them and the root, conducting from the latter to the former, 

 animal and vegetable substances, the salts and earthy matter 

 which the radicles by their mouths, suck up for the nourishment 

 of the plant. 



If a plant be watered by any coloured liquid, the stem will in 

 time, shew that this fluid has ascended into it. This organ also 

 contains asetof vessels which carry downwards certain juices, 

 which have passed through peculiar processes in the leaves of 

 the plant. 



But of the circulation of fluids in the vegetable substance 

 we shall speak more particularly hereafter. Our present ob- 

 ject is, to describe the external appearance of the vegetable 



* In the vicinity of Troy I have seen a very beautiful species of the Pterox- 

 pora, growing upon a branch of the whortle berry. Its colour was a bright 

 crimson, which contrasted finely with the white flowers, and green leaves of 

 the plant on which it grew. 



Air plantsProper time to collect roots for medicinal purposes Trunk-- 

 Its use. 



