SOTJKOES OF NUTRIMISNT. 



25 



pended nearly as fast as it is collected. Only enough is 

 laid by to sustain the process of flowering, and when that 

 is over, the plant dies from mere exhaustion. 



146. Biennial Eoots. — These in the first season 

 merely put forth a tuft of leaves; and all the extra 

 nourishment which the roots absorb is stored away in the 

 large, fleshy knobs, tubers, or other receptacles, that 

 always distinguish such roots. This is generally in the 

 form of sugar, starch, or mucilage. In the second year's 

 growth, the plant clothes itself with a stem and leaves, 

 flowers, and ripens seed. These processes are almost 

 entirely maintained by the accumulation of the previous 

 year ; and thus the root, having no further supply, be- 

 comes exhausted, and dies. The Beet, Carrot, Radish, 

 and most of our esculent roots, belong to this class. 



147. Perennial Roots. — All trees and shrubs, 

 and many herbaceous plants, have perennial roots, or 

 such as live and grow many years. Those belonging to 

 arborescent and shrubby plants are woody, and, like the 

 stem in such growths, they have but a very small portion 

 of their tissue in an active state at any given time. The 

 wood is formed in the same manner as that of the stem, 

 but it has no part in the proper office or functions of the 

 root, which are vested entirely in the fibrils. These 

 last are, in all cases, temporary, either existing only in 

 the youth of the tissues which they clothe, or at most to 

 the end of the growing seasCn. But they are always 

 renewed in the young and vigorous parts, and wake with 

 the waking season, to the fulfilment of their proper 

 work. 



148. Herbaceous Stems — even those of our pe- 

 rennial herbs — are always strictly annual ; for since 

 they cannot endure the severe cold of the winter, in tem- 

 perate climates, they die down to the ground with the 

 coming of frost ; while the perennial roots, with their 

 latent juices, remain closely enveloped in their earth- 

 mantle, until Spring returns and calls them forth, when 

 they send up new stems, and appear with all the freshness 

 of a new life. Thus year after year renewed, they con- 

 tinue to put forth yearly their new stems, crowned with 

 new flowers and fruit. For this reason, small, shrubby 

 perennial stems, on being acclimated at the North, 

 change their habit, and become annual. Thus the Nas- 

 turtion, which is a perennial shrub in Peru, where it 

 is a native, in our climate becomes an herbaceous an- 

 nual. 



life of Annual Eoots. Biennial. Perennial. Perennial Ilorbs. Instances 

 of ciuOi. 



CHAPTER XII. 



BOUECES OF NUTEIMENT. 



149. The Root, in its normal position, may be con: 

 sidered as fixed in the soil, but it is occasionally found 

 floating at large in water, as in the Duck-weed, and many 

 Sea plants. Sometimes also it germinates without coming 

 in contact with either earth or water, and continues to 

 maintain its life in the open air. Again, it will strike 

 into the tissue of other plants, and live on the assimilated 

 material which it there finds. 



150. Roots that live in the water are called Aquatic 

 Roots ; those which shoot in the air. Aerial Roots ; 

 those which live on other plants. Parasitic Roots; 

 and those which are used merely as mechanical support, 

 to fix the plant to the surface on which it grows, Epi- 

 phytic Roots. 



151. Aquatic Roots are generally distinguished by 

 very numerous, long, slender fibres, the use of which is 

 apparent ; for, living in a rarer medium than the soil 

 affords, they thus present a much greater extent of sur- 

 face to the surrounding element, and the means of obtain- 

 ing food are thus multiplied. Sometimes these roots 

 are quite free, and float at large, as in the Water Chick- 

 weed ; at other times they send down long processes! and 

 establish a connection with the soil, as in the White 

 Pond Lily. 



152. Aerial Roots. — These are sent forth by the 

 stem at a distance from the ground, which they finally 

 reach and penetrate. The Mangrove, inhabiting the 

 low marshes which form the shores along the mouths of 

 most of the large tropical rivers, is able to sustain itself 

 in its unstable position by its strong aerial roots. These 

 are sent forth from different heights on the stem ; and 

 after reaching the ground they establish themselves, and 

 form a kind of frame-work, on which the tree stands, 

 securely braced by the interlacing of its woody fibre with 

 the roots and fibres among which it is established, while 

 at the same time the water obtains a free passage through 

 the lattice-work thus formed. These roots are natural 

 layers, and again send forth stems, and thus whole 

 forests are produced. This tree is represented at fig. 13, 

 but not very perfectly, for the aerial roots which it drops 

 down from the branches, as well as the main stem, are 

 not prolonged sufficiently to be conspicuous, nor are their 

 gradations preserved. In the Screw Pine (Pandanus) 

 we find the same habit, which is quite as admirably 

 adapted to its condition, as you wUl see at flg. 12, where 



General subject Normal position of ttie Eoot. Exceptions, Koots that 

 live in water, what? On other plants? In the air? Used only to fix the 

 plant ? Describe Aquatic Boots. Aerial Eoots. Eemarkable instances. 



