CHAPTER IIL 
THE ROOT. 
MORPHOLOGY. 
A SUNFLOWER or bean-plant may be regarded as consisting of 
two slender cones placed base to base (fig. 2). One of these, the 
primary stem, grows upwards ; the other, the primary root, down- 
wards. When such a main axis forms the most prominent part 
of the root, it is said to be a tap-root,.and this is very strikingly 
seen in the carrot, turnip, and radish. The primary root 
generally possesses numerous branches, and these may be re- 
garded as so many slender cones attached by their bases to the 
main one. These secondary roots are commonly in the form of 
fibres. But the primary root is very often extremely short, and 
in that case (e.9., grasses) the plant is fixed in the ground by 
means of adventitious roots (fig. 4), which usually grow from the 
stem, but may also arise from the leaf-stalks or leaves. Such 
roots may also be present in addition to the primary and secondary 
ones, as, for example, in the ivy, where they are used for climbing. 
The “striking” of cuttings means the development of adventi- 
tious roots from the end of a piece of stem pushed into the soil. 
The majority of roots are underground,.but aquatic plants possess 
water-roots, and air-roots are also known. These last may be the 
only ones present, as in many tropical orchids; or, as in the ivy, 
they may exist in addition to roots of the ordinary kind. The 
orchids in question are epiphytes, that is to say, they simply live 
on other plants, but not at their expense. Plants exist, however, 
such as the clover-dodder, and mistletoe, in which the roots are 
parasitic, penetrating and deriving nourishment from the tissues 
of other forms. 
Young roots are white or pale in colour, old ones generally 
brown. Under no circumstances is the green colouring matter, 
chlorophyll, present. Leaves are never found upon the root. 
The external form of a root system depends mainly on three 
things: (1) the presence or absence of a tap-root; (2) the nature 
