xxxviii INTRODUCTION TO BOTANY. 



absorbs a part of the fluids destined for nutrition and repair ; 

 the stem transmits these fluids into all points of the vegetable, 

 while the leaves perform the same office as the roots in the 

 earth, and seem at once organs of absorption and of exhalation. 



Of the Root. 



A remarkable character of the root is, that it never turns 

 green, in its tissue, when exposed to the action of air and light. 

 Roots serve commonly to fix plants in the soil, and to draw 

 from it a part of their nourishment. 



The division of vegetables into annuals, biennials, and per- 

 ennials, is subject to variation, from climate, temperature, 

 situation of a country, and cultivation; for example, annual 

 plants will not uncommonly vegetate for two years, and even 

 more, if placed in a suitable soil, and protected from the cold. 



Roots absorb from the earth the substances, serving for the 

 growth of the vegetable. It is only by the extremity of the 

 minutest fibres of the root, that absorption is effected. Some 

 maintain that the fibres are terminated by small vesicles or 

 spongioles; others, that they are terminated by a species of 

 open mouths. To prove that the extremities alone perform 

 the office of absorption; immerse a radish or a turnip in 

 water, by the extremity of the rootlet, which terminates it, 

 it will shoot forth leaves, and vegetate. If the lower extremity 

 be not immersed, it will not shoot out. Roots have a marked 

 tendenc}^ to grow in the direction of veins of good soil. They 

 possess a natural and invincible tendency to move towards the 

 centre of the earth : this is particularly observable during the 

 germination of the embryo. From different experiments, 

 mentioned by Richard, it appears that the roots are directed 

 towards the centre of the earth ; not because they contain a 

 less elaborated fluid, nor because they are attracted to it by 

 the moisture or even the nature of the earth; but by a sponta- 

 neous movement, an interior force, a kind of subjection to the 

 general laws of gravitation. Some vegetables, however, seem 

 exempt from this law ; for eyi?ixn^\c, parasitical plants, and the 

 mistletoe, (viscum album,) in particular. This plant shoots 

 out its radicle (rootlet) in whatever situation chance may 

 place it ; and it has a constant tendency to shun the light. 



