RUDIMENTS OF THE NATURAL SYSTEM OF BOTANY. 
113 
tree, but this is quite accidental. Shrubs differ from trees in having a great 
number of dwarf stems individually connected with the roots, and constituting a 
low bush. Like trees, they have a hard, woody, durable axis, but of a much less 
diameter and altitude. Suffruticose or subshrubby plants are such as have a ligneous 
stem at the base, losing annually all their upper portions. Herbaceous" plants 
possess a still more fugitive axis, as every part of their apparent stem decays yearly, 
to be supplanted in the following season by new emanations. Those stems which 
are short, thick, or fleshy, and creep along on or near the top of the ground, bearing 
many shoots on their upper surface, and roots from beneath, are called rhizoma. 
They are found in some Tridacese, OrchidacetB, and other related orders, but are 
never to be discovered in any exogenous plants. Bulbs and corms, which are both 
peculiar forms of stem, belong likewise to Endogenae, and assist in isolating several 
orders. Bulbs comprise that kind of depressed conical stems which are composed 
of successive series of succulent layers or scales ; each of these being analogous to a 
dilated incrassated petiole or leaf-stalk, very often developing leaves on its apex, 
and producing buds (which in time expand into other bulbs) from the axil at its 
base. The tulip and onion are excellent examples. Corms, again, are much 
flatter, quite solid, without any separate scales, and reproduce themselves from the 
summit. The most common illustrations are the Crocus and Ixia. 
When the stems of Vascular plants have attained a few inches in height, they 
put forth a quantity of thin, flat, variously-formed dilatations from the bark, popu- 
larly designated leaves. These, by being the most highly diversified of all vegetable 
organs, and at the same time so exceedingly palpable to the senses as to need no 
examination by optical instruments, are, where their peculiarities are established 
as a guide, the best criteria for ascertaining the precise order to which a plant 
belongs. The number and direction of their veins, their position with respect to 
each other, the extent to which they are divided, and the existence or lack of little 
pellucid dots, which, when held up to the light, exhibit a much thinner and almost 
transparent tissue, are a few of their characters that impart distinctiveness to 
certain natural orders. 
It is no trifling argument in favour of the natural system that nature has given 
to many plants composing its entirely artificial orders, so striking a similarity in 
the conformation, outline, or venation of the leaves, that, independently of the 
floral or fructiferous organs, which are not seen on some species except when in a 
natural state, their exact place in the arrangement may be ascertained through such 
means alone. When we arrive at the description of particular orders, this fact will 
be at once perceived, and, we would hope, duly estimated. Some plants, besides 
having the ordinary leaves, develop one or more small appendages called stipules, 
at the lower end of each, which frequently serve to detach individual tribes. They 
are not to be identified with the lateral expansions in the leaf-stalk of the rose, but 
always proceed immediately from the stem, and are, indeed, real leaves in a very 
stunted or deformed condition, 
VOL. VII. NO. LXXVJr a 
