4 THE VEGETABLE WORLD. 
forms tufts or branches of a delicate pale green, attaching itself 
to apple-trees, poplars, and a number of other trees. Some roots 
appear, moreover, to have no other function than to fix the plants 
to the soil: they seem to contribute nothing to their nourishment. 
In the Museum of Natural History of Paris, 
there has been for some years a magni- 
© height, which has been growing vigorously, 
throwing out enormous branches with great 
rapidity. Its roots are shut up in a box 
of forty inches square, filled with earth, 
which has never been renewed and never 
watered. It is therefore evident that in 
this case the roots have little to do with 
the nourishment of the plant. Other in- 
stances confirm these inferences. ‘ In this 
country, where six months passes without 
a drop of rain falling,” says Auguste de 
St. Hilaire, “I have seen, during the dry 
season, cactuses covered with flowers, main- 
taining themselves on the burning rocks 
by the aid of a few weak slender roots, 
which sink into the dried-up humus which 
has found its way into the narrow clefts of 
big. 5.—Duck-weed (Lemna). 
nourished, to a large extent, through their 
roots. Other plants, as the Screw-pine (pandanus), and the 
Mangrove-tree (r/izophora, root-bearer, from its habit of emitting 
roots from the stem, which descend until they reach the ground, 
when they bury themselves in the soil),—these are sometimes 
called—not very correctly however—aerial roots. 
The multiplication of roots takes place, sometimes by their 
elongation and thickening, as in the Carrot, Turnip, and Beet 
(Fig. 6). When short and slender, natural rootlets, named radi- 
cles, are emitted, or rootlets which accompany the descending 
body ; this is the tap-root. Sometimes the root is entirely com- 
posed of axils, more or less numerous, and nearly of the same size, 
which unite at the col/um, or point of juncture, of the stem and 
ficent Peruvian cactus, of an extraordinary 
the rock.” Nevertheless, most plants are — 
