صور الصفحة
النشر الإلكتروني

resultant of two forces; which in this case, we assume to be the current of the wind, and terrestrial magnetism? So far at least, we are certain, that those long lines of wane-clouds very frequently lie in directions corresponding or nearly corresponding with the magnetic meridian ; and if magnetism has no influence over them the coincidence must be confessed to be singular and unaccountable.

It would be wrong, however, to venture upon any positive assertion of this theory or rather speculation, in the deficiency of well ascertained facts; but from the analagous arrangement between the wane-clouds figured above, and the streaks of the Aurora Borealis, which is also supposed to be connected with magnetism or electricity, we think, that farther investigation may elucidate the dependance of the phenomenon on the same

The Aurora Borealis indeed, is almost always in the direction of the magnetic meridian, while the wane-clouds in question, so far as we have remarked, are more under the influence of the current of wind blowing in the plane of their stratification. *

CAT WHICH CAUGHT SWALLOWS ON THE WING. -We have frequently remarked the surprising rapidity with which beasts of prey pounce upon their victims, but the most striking instance which we recollect of, this was that of a cat, who caught swallows on the wing. It was in the spring, when insects, in consequence of the cold, fly low, and of course the swallows are forced to hawk for their prey by skimming the surface of the ground. The wily cat, taking advantage of this, stretches herself upon a sunny grass plat, with her legs extended

* J. Rennie, in Mag. Nat. Hist, vol. i.


as if she were dead; the flies collect about her, as fljes always do when they can find any animal as patient as my uncle Toby to endure their buzzing and tickling. The simple swallows, dreaming of no harm, and thinking they can here make a good meal,---dip down from the barren air,—dart with open bill upon the flies; when puss, perceiving her prey within reach, makes a spring like a flash of lightning, and strikes down with her paw the poor thoughtless swallow. The best marksmen know how difficult it is to shoot a swallow on the wing ; but the cat found her patience, cunning, and rapidity well rewarded by her unerring success whenever a swallow ventured within her reach.

DIFFUSION OF SEEDS.—The economy of Providence in distributing seeds, may now be remarked in those of the Dandelion (Leontodon taraxacum which are every where to be seen floating about on the air, supported by their feathery down. It is not to be supposed, that half of these ever fall upon spots favourable to germination; but when so great a number of them, and of their congeners of the class Syngenesia, are scattered about by the winds, it almost raises the chance to certainty, that some of them will fall in spots where before there has been none, or only a scanty vegetation : on the tops of walls, for instance, where a thin stratum of soil has been formed by the decay of the winter crop of mosses. The process of the formation of such soil is exceedingly interesting, and may be observed on a small scale even in cities, on brick or stone walls. First, there is the green incrustation called byssus, by Linnæus, but recently proved to be the primary germination of several species of mosses, such as polytricha and tortulæ. When this


decays, a very thin layer of vegetable earth is formed, which affords a scanty support for the roots of the next year's crop of mosses; and in process of time, soil is formed of sufficient depth for Draba verna, and other wall plants. A singular contrivance is conspicuous in one of our wild cresses (Cardamine impatiens), as well as in the balsums, and in touch-me-not (Impatiens Noli-me-tangere)-a native plant of the same genus. In all of these, when the seed is ripe, the valves which enclose it are so constructed, that by the influence of the sun's heat, they open with a sudden jerk, and throw the seeds to a considerable distance. The same effect is produced sooner, and with more force, when the ripe seed vessel is touched by the hand, or by any accidental waving of the leaves against it. Were we disposed to refine upon the final cause of this,-a subject very ready to mislead), we might say, that this jerking of the seeds was contrived not only for their diffusion, but for their preservation from birds and insects,--since the instant that these should begin to devour them, the springs of the valves would be thrown into action, and the seeds scattered about before a single one could be secured for a meal. In the wood-sorrel, (Oxalis acetosella) as well as in the horned-sorrel (0. corniculata) the structure of these valves is very beautiful, but no description could do justice to it, not even with the aid of figures. The first, however, abounds in most woods, and the latter where it has been introduced as a flower, soon becomes, from the circumstance under consideration, a very troublesome weed.

One of the most beautiful contrivances for the diffusion of seeds occurs in various species of violets.

". The

seeds of this order of plants are contained in a capsule of a single loculament, consisting, however, of three valves. To the inner-part of each of these valves the seeds are attached, and remain so for some time after the valves, in the process of ripening, have separated and stood open. The influence of the sun's heat, however, causes the sides of each valve to shrink and collapse, and in this state, the edges press firmly upon the seed, which, from being before apparently irregular in its arrangement, comes into a straight line. The seeds, it may be remarked, are not only extremely smooth, polished, and shining, but regularly egg-shaped; so that, when pressed upon the collapsing edges of the valve, it slides gradually down the sloping part of the seed, and throws it with a jerk to a considerable distance. There is another part in the contrivance of Providence, for the same purpose, in the violaceæ, worthy of remark. Before the seed is ripe, the capsule hangs in a drooping position, with the persisting calyx spread over it like an umbrella, to guard it from the rain and dews, which would retard the process of ripening : but no sooner is the ripening completed, than the capsule becomes upright with the calyx for a support. This upright position appears to be intended by Providence to give more effect to the valvular mechanism for scattering the seeds, as it thus gains a higher elevation (in some cases more than an inch) from which to project them; and this will give it, acccording to the laws of projectiles, a very considerable increase of horizontal extent.

“ Some ripe capsules of a fine variety of Viola tricolor, which I placed in a shallow pasteboard-box, in a drawer, were found to have projected their seeds to the distance

of nearly two feet. From the elevation of a capsule, therefore, at the top of a tall plant, I should think these seeds might be projected twice or thrice that distance."*

MIGRATION OF EELS.-The migration of fish, which occurs at particular seasons, according to difference of species, may, during the present month, be remarked in the case of eels in streams wbere they abound; but as it usually takes place in the night, it seldom attracts attention. In cloudy weather, however, they often continue to run, as it is termed, during the morning. We once, and only once, remarked this, about ten years ago, on the 13th of May. The river Clyde was embrowned at the time in consequence of a recent fall of rain, which may have partly induced them to continue running after sunrise. Their line of march, if we may call it so, was about a foot or more from the edge of the bank, with which they kept nearly parallel, and their column might be about six inches broad. The eels themselves were all of one size, about as thick as a crow-quill, and about three inches long. They kept so closely together, that there might be, we should suppose, some hundreds in a foot's length of the column. What was no less singular, the column itself appeared in its whole extent to be of uniform breadtb, as if it had been regulated by the parallel lines of a mathematician. The length of this column we had no means of ascertaining, but it must have been considerable, as we traced it for more than half a mile; and during several hours which we observed it, the run continued undiminished, and proceeded at a velocity, as nearly as we could estimate by the eye, of half

* J. Rennie, in Mag. Nat. Hist. i. 380.

« السابقةمتابعة »