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Show 280 FORESTS OF AUSTRALIA. cession. we look in vain for the buds of sprii~g w_h~ch 1 are at once the most beautiful and the most mspirmg of nature's proJuctions. d Even the leafless a-roves have their charms ; an he who has never studied it in the winter has no proper knowledge of the beauty or even the _form of a tree. There is fully as much character m those permanent parts as there is in ll.e ~ea~es or the flowers. There ts a character of specws m the bark, and there is a character of age. ln th~ you!lg shoot 't . ooth. but as the tree gets old It IS nfteu and ~ht~:.m Exc~pt it be some of the sycamores, a_nd the are not natives, there are not trees th_at 'Y1t_h us innually cast their bark. In son_1e countnes It IS different. In New-Holland, for mstance, all t~w s ecies of Eucalyptus, and they compose the prmclpal forests, cast their external bark down to the white liber every year ; so that, though t~e leaves are evergreen, there is a " [;-11 of the bark answer-ina- to our "fall of the leaf. . . When we compare those two ?peratwns, an~ then consider the difference of the timber, we gam _one oint of knowledge in the eco.nomy of v~getatwn. Prhe dismantling of the leaves IS a protectiOn to the 1- nt as a whole. lt presents a smaller s.urface to Eh! wind, and the whole of it is wrapped up m a cl?se mantle from the cold. ~he. juices which, . durm.g the summer action, were hq~:nd, b~come firm m thmr consistency and diminished m the1r bulk. . The bark is elastic and not only follows the lessemng of .the stem but ~o-operates in bringing about that lesse!ung. This 'condensation in the wood of the tree, and ~t ~x~ tends to all the wood which is in a st?-te of activ1ty, necessarily generates heat, for heat IS produced m all cases of condensation; and thus, the colds of early winter ~ich would destroy leaves, unless those leaves bad the glossy epidermis of evergreens, has no injurious effect upon the stem. Indeed, the ~pidermis \_)f an evergreen leaf has more resemblance EVERGREENS. ?Sl to that of a twig of the first or second year than to that of a deciduous leaf. The cold acts in it in nearly ~he same way, and it becomes rigid; so that there is little or no action of any kind in it during the winter. And, as even the evergreen leaf is but a , temporary organ, which accomplishes one purpose ~ and then decays, the leaf of the evergreen does not revive in the revival of spring. If, after the winter is over, the leaves of a common evergreen-those of the laurel, for instance-be f tried by a proper test, it will be found that their vitality is gone, although their colour remains. The very best test of life in vegetables, as well as of health in animals, is the thermometer. The living thing, be it what it may, has always one temperature which is the most favourable to healthy action, and it struggles to preserve that; but when the principle of life fades, the mere matter obeys the laws of matter; and thus, when the evergreen leaf has ceased to perform its functions as a leaf, it has no longer the uniform temperature of the growing plant, but gets heated in the sun and cooled in the shade, in the same manner as though it were a portion of inorganic matter. If the experiment is made after the young leaves are expanded, but before the old ones show any discoloration or other symptom of decay, and made when the sun shines brightly, the contrast is very striking; so much so, that an instrument is quite unnecessary ; for the young leaf feels cold, and the old one warm. This shows that all action in the old leaf has ceased ; because it is the action, the evaporation of moisture at the surface of the leaf which preserves its coolness. ' In all cases where there is an an al leaf there is also an annual plant. In trees which l~st for years that is a very beautiful study; and if we could separate the oak which has stood a century into the hundred oaks that have been produced in the sue Aa2 |
