OCR Text |
Show 296 LIGHT REGULATES VEGETATION. grow altogether in the light, and it is not' edible, neither will it make into starch. Its qualities approximate those of a leaf or a stone. Celery, and the other plants which are generally made use of in a blanched state, are unfit for being eaten if the light has free access to them ; and generally where mere nutriment is the object, it is best attained in the shade. Forest trees of which the cotyledon& rise above the surface, and perform the functions of leaves, are not so much deteriorated by the nursery mode of sowing, as those of which the cotyledons remain below, but still they are all injured less or more, so that no planted tree forms timber equal in quality to that of naturally sown timber. The planted pines are a very striking instance of that ; for in those districts where the natural pines afford very excellent and durable timber, the planted ones, even when the cones have been taken from the natural trees, are spongy and soft ; and the " hearty" wood of them does not last much longer than the sapwood of the natural trees. Want of the proper action of light at " starting" is not the only injury which timber trees sustain, by the way in which they are grown for the market. They are sown so close, that while they remain in the seed-beds they want both air and light. A seedbed of pines, in the early stage of their growth, :resembles a plat of moss more than any thing else ; and when it is considered that, in the situation where they are native, the pines stand singly and are exposed on all sides to the action of very keen air, it must easily be seen that they cannot acquire their due strength when huddled together to the number of many hundreds on a square foot. Those who are familiar with pine forests, or pine plantations, must be aware that the seeds of the cones never germinate under the thick shade of the trees, and ~ow up so as to form an underwood in the forest. SUCCESSION OF PLANTS. 297 Cones in abundance are produced every sPason, but they contribute chiefly to the food of tne animal inhabitants, and it is only where a blank occur:s, from the decay or the casual destruction of a tree, that young- plants rise to fill it up. There are, indeed, few or no trees of which the young plants grow and form underwood, while the old ones remain filling the air above. Nor would it be in accordance with our general observation of nature if they did. The young of no tribe, vegetable or animal, are the destroyers of the old; they merely come on, in succession, when they are required; though the germes of all are exceedingly numerous, so that there never is room on a fit soil at the proper season, without the plant appearing to fill it. But man comes in with his nursery-bed; and though he cannot be said to overstock the country (for there can hardly be too many trees-and there are numerous and wide wastes in England, where it is disgraceful that there are not millions), yet the nursery-bed is overstocked, and the consequence is, the dry rot in oak, and general rottenness. and want of strength in all timber. The inferiority of planted timber is often attributed to the act of transplanting ; but though that may have a considerable influence upon the growth, it cannot have so much on the quality of the timber. Trees that have long top-roots, as the oak has, cannot be transplanted without injuring them, and injuring them often to a considerable extent ; but still that is only a mechanical injury, and can affect only the size and appearance of the trees. The economy of vegetables has not been carefully and extensively enough examined, for enabling us to say what effects variously tainted atmospheres have upon forest trees, or even upon vegetables of any desc.ription; but enough is known to let us see that t.Qey must be very pernicious. The air of the sea · is very hurtful to all plants that contain potass,. |