220 
THE CABINET OF NATURAL HISTORY 
to seek for food, when the mountains are covered with snow. 
The American species is remarkably swift, never taking 
shelter when pursued, and is capable of taking astonishing 
leaps; Captain Lewis measured some of these, and found 
their length to be from eighteen to twenty-one feet., The 
variabilis is said, on the other hand, to be rather slow in 
its motions, and, when alarmed, to seek for refuge in clefts 
of the rocks. Warden, however, states that the virginia- 
nus, when pursued, will retreat into hollow trees. 
They, like all the Hares, are very prolific, the female 
having several litters a year, of five or six leverets at a time. 
ON THE GROWTH OF TREES. 
One of the most obvious contrasts presented by the vege- 
table kingdom, is between the tribes that rapidly expand 
their foliage, and push up their flower-bearing stems, and 
by bringing their fruit to perfection, fulfil the purpose of 
their creation in the space of a few months, or even weeks, 
and those monarchs of the forest which bear aloft their ma- 
jestic branches in the air, and see centuries passing by them, 
while generation after generation of herbs, and even men, 
are perishing at their feet. One would think that if any 
thing could indicate a difference of organization, it would 
be peculiarities like these. In fact, if we examine one of 
these vegetable colossi, which storms or other accidents have 
levelled with the earth that was so long overshadowed by its 
branches, we perceive that its interior consists of a solid, 
compact, homogeneous substance, which seems to be ana- 
logous to nothing in the annual plant ; we also see, how- 
ever, that a section of this substance is marked by concentric 
circles. In order to ascertain the origin of these circles, it 
is necessary to revert to the seeds, which such a tree pro- 
duces in vast abundance. There we discover the same parts 
as in the annual plants; two cotyledones; a cylinder, which 
attempts to fix itself in the earth by the production of roots; 
and an intermediate bud. The impulse once given to its 
development, this seed, with its apparently feeble resources, 
will become in the lapse of years and ages similar to that 
giant which produced it. In the leaves and buds consist the 
sources of its magnitude; the former being under the neces- 
sity, on the one hand, of coming into contact with air, and 
on the other, of establishing a communication with the soil, 
establish the action of vegetation. The first year passes on 
as in the annual plant, except that the parts of the tree are 
unfolded with less rapidity, and that the buds present nei- 
ther flowers nor fruit, but a tree covered with scales. Upon 
the arrival of winter the annual perishes, the tree loses only 
its leaves. As soon as the season again becomes milder, 
vegetation, which had been suspended, is renewed; the 
buds insensibly expand, and the unfolding of new leaves 
gives a new life to the plant; each of these leaves is accom- 
panied by its bud. Thus each successive season, producing 
a mass of foliage, which increases by a rapid geometrical 
progression, and an equal number of new buds, occasions 
the formation of a new body of ligneous substance, which 
overlays the whole body, and thus forms the whole tree in- 
to a kind of cone. 
The whole mass of the wood is thus composed of thin 
successive cones. They are easily perceived in many trees, 
and it is they which form those concentric circles observa- 
ble in a trunk cut across. Each circle, depending wholly 
upon the increase caused by the return of successive seasons, 
becomes a sure testimony of the age of the tree. 
The principal part of our trees exhibits these laws of de- 
velopment. The buds may be more or less apparent; and 
the scales which enclose them may be more or less nume- 
rous, being increased in number in proportion to the greater 
sensibility of the organs which they enclose. For a more 
sure protection, the scales are often covered with glutinous 
or resinous exudations. But even with this safeguard, the 
fostering hand of nature does not rest. Thick furs are fre- 
quently interposed during the winter among the buds, and 
thrown over the tender shoots. 
By this means the buds remain safely upon the tree. We 
generally remark one which is a termination of the branch 
and which will the following year prolong the branch in its 
original direction; all the others are seated at the axillae of 
the leaves. 
Trees present many peculiarities, which depend upon 
their woody state. The pith, which occupies the centre of 
young plants, disappears in trees. It is probable that, be- 
sides the increase in diameter which takes place externally, 
some peculiar operation goes forward in the inside, and that 
the solid layers of wood compress the pith in such a way as 
to leave scarcely any traces behind. Around it vegetation 
is evidently maintained for a long time, as is shown by the 
green tinge which surrounds it. Larger and more obvious 
vessels are placed about it than elsewhere, and constitute 
what is called the etui medullaire by the French, which 
there is reason to think is one of the most important acces- 
sories of vegetation. 
The wood does not at once arrive at that solidity which 
it subsequently possesses, but acquires it by slow degrees, 
from the centre to the circumference. For this reason the 
external layers are much less compact, and paler than the 
internal; they are called the alburnum. Dutrochet accounts 
for this difference in the old ard new layers of wood with 
his usual sagacity. He is of opinion that a portion of the 
