Ill 
said to be fibrous. In some cases, however, the vessels of the root 
form a thickened mass, from which the absorbent fibres diverge, 
and to which various names are given according to its shape and 
proportions; the most common varieties being the tap-root, where 
it descends in a tapering form into the ground, as in the Radish 
and Parsnip, and the tuber, in which it forms several more or less 
irregular, rounded masses, as in the Orchis and Potato. In the latter 
vegetable, however, the tuber is considered by botanists to be a 
modification of the stem, and not a root in the strict sense of the 
word. The same is the case with the leafy bulbs of the Lily and 
Onion, and the corm or solid bulb of the Crocus, and some other 
subterranean portions of plants to which the name of root is ap¬ 
plied in common language. In this work the word is used in its 
popular meaning. 
The stem is that portion of the plant which, rising from the 
root, supports the leaves and flowers. In some plants it is wanting, 
being represented only by the thickened rim or apex of the root 
from which the leaves and flower-stalks proceed, as in the Dande¬ 
lion; in other instances it creeps along the ground, as in the Iris, 
when it is called a rhizome. The stem is in all cases formed of 
the vessels that descend from the leaves and flowers to the root, 
and in which the sap circulates, and the various juices and secre¬ 
tions of the plant are elaborated. In some plants it dies down 
every year, fresh stems rising to supply its place the following 
season; the plant is then termed herbaceous. In other vegetables 
it becomes a permanent portion of the plant, the leaf-buds con¬ 
tinuing to send down their fibres through it as long as growth 
lasts, and thus producing the substance we call wood; the plant is 
then a tree or shrub. Whether the stem be herbaceous or perma¬ 
nent, the buds which produce the leaves and branches are formed at 
certain points on its surface called nodes, where a change of direc¬ 
tion takes place in the fibres; the space between being termed an 
internode or joint. 
b 2 
