CHAPTER V.

THE ROOT.

EXERCISE LI.

Tap-Roots and Fibrous Roots.

THERE are two classes of roots, called tap-roots and fibrous roots, which differ from each other in the way shown in Figs. 234 and 235.

FIG. 234.

FIG. 235.

Tap-root.

Fibrous Root.

Fig. 234 represents a TAP-ROOT, which is seen to be simply a continuation of the stem downward.

In Fig. 235 the stem is not continued downward as a tap-root, but sends off rootlets or fibres at the outset. It is hence called a FIBROUS ROOT.

CON'ICAL ROOTS are tap-roots, which taper gradually downward, and so are shaped like a cone. Fig. 236.

FU'SIFORM, OR SPINDLE-SHAPED ROOTS, are taproots enlarged in the middle of their length, and tapering toward both ends. Fig. 237.

A NAP'IFORM, OR TURNIP-SHAPED ROOT (Fig. 238), is a tap-root, more or less globular in form.

The kinds of tap-root illustrated in this exercise are equally continuations of the stem, with that shown in Fig. 234. By reference to Fig. 116, it will be seen that these stems are made up of nodes, and are just as really stems as those in which the intervals between the nodes are considerable.

In MONIL'IFORM ROOTS (Fig. 240) some of the fibres have numerous small swellings, that succeed each other so as to look like a string of beads.

In FASCICULATED ROOTS (Fig. 241) the fibres become swollen along their length, and look like a bundle of fusiform roots.

When some of the rootlets of fibrous roots become fleshy and enlarged, taking the form shown in Fig. 242, they are called TUBERCULAR Roots.

NOTE. It is not difficult to see that the moniliform root is only a fibrous root, in which regular portions of the fibres have become swollen. When all these swellings unite in one continuous enlargement, we have a fasciculated root (Fig. 241). When the swellings are shortened and globular (Fig. 242), we name them tubercular roots, but their resemblance to the fibrous root is still apparent.

The questions about roots suggested by this chapter are, first, is the specimen in hand a tap or fibrous root? The answer may not always be easy, but the pupil will exercise his best judgment upon it. If it be fibrous, however, say so; if any modification of fibrous, say which, and similarly if the kind be a tap-root. For aid in describing roots, we must refer pupils to the exercises in plant description, which follow.

There is usually a certain balance between the size of the root and stem of a plant; but sometimes the root is very small compared with the stem and branches, and sometimes it is large. Roots may also be loosely attached to the soil or firmly planted therein; they may be spreading near the surface, or may grow directly downward, and such facts are worthy of note in root descriptions.