94. BOTANY 
stems as round, like the oak and pine, square, like the 
bean and mint, triangular like most sedges, and ribbed 
like the lancewood, does not achieve much. 
The division into annuals, enduring only for one 
year, biennials lasting for two years, and perennials 
lasting for more than two years, is good as far as it 
goes, but refers to the plant as a whole rather than 
to the stem exclusively. Then again we may dlis- 
tinguish herbs, shrubs and trees: herbs, soft and succu- 
lent in all their parts, shrubs, woody, but only a few 
feet in height, and trees, also woody, but growing to 
a great height and not generally branching near the 
ground. It is obvious, seeing that the chief distinction 
between shrubs and trees is merely one of size, that it 
is sometimes difficult to know in which class to place 
a particular plant. 
Probably the most convenient way of classifying 
stems is to place in one class those that are above, and 
in another those that underground. The former, which 
we shall call aérial stems, may be divided into three 
eroups—erect, climbing, and prostrate. 
Erect stems are the commonest of all, for an upright 
branching stem is, under ordinary circumstances, the 
best means of displaying leaves, flowers and fruit. 
Such stems we see on every hand, in parks, forests and 
orchards, and though all are solving for. themselves 
the same problem of securing for their leaves the 
maximum of light and air, yet no two are alike. 
We have the pinus insignis and the young kauri 
with their straight tapering trunks and cone-shaped 
crowns, the puriri and the oak with branched and 
spreading tops, the willow with its pendent branches 
hanging nearly to the ground, the poplar, spindle 
shaped, compact in form with branches pressed close 
to the central stem, and the pohutukawa with contorted 
branches reaching out over the water from the face of 
some high cliff. The characteristic form of the mature 
