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 tlie 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 witli 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 tlie 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- 

 Yelopment. 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 whicli 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 axillse 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 and new layers of wood with 

 his usual sagacity. He is of opinion that a portion of the 



