Are the sheaths found on certain radicles strictly confined to monocotyledonous plants. There is this certain about them, that they depend on the presence of vascular tissue, from which the radicles or the divisions of each root originate: see young Hyacinth roots, grown in water.
Although the sheaths cannot exist without a positive cuticle, their existence does not depend so much on its presence as on the direction of the adhesive powers of its component parts: witness certain forms of Marchantiaceæ, and the vaginate forms, as Azolla, Lemna, etc. Also the sheath may not have adhesive powers at its apex to prevent the escape of the radical at that point: witness Hyacinth roots? We may imagine a case in which the primary radicle may be without a sheath, while its divisions shall have them, this depending on the want of adhesion of the cuticle over the original one.
The emerged and immersed leaves of plants are well worthy of examination, since Microphytum proves that stomata do not depend on the presence of a cuticle as Brongniart supposes: their presence is united with, or allied to an amount of density in the cellular tissue, sufficient to prevent the due aeration of the inner cellules, without direct communication with the atmosphere. Vide Musci!! Hence the inner tubes of the leaves of the generality of aquatic plants, (exception Eriocaulon fluitans.)
What is the cause of the plurality of radicles in certain species of Lemna, and their blank in others? It will be necessary on this point to examine well the sheaths of Azolla, and to look at the Mergui Æschynanthus.
The formation of Affghanistan is very curious: it consists of a wide extent of country, variously elevated steppes being separated by ridges usually very accessible, generally isolated. The mountainous part varies as to its formation, but there is no variety in the declivities and acclivities forming the lower elevations, which are composed of conglomerate; nor is there much in the usually narrow strip at the lowest portion of each steppe or valley, which is very generally the only cultivatable portion.
In the Khyber ghat the ridges are either of limestone or slaty rocks, between which conglomerate occurs of various thicknesses; this being dependent on the angle of the mountains forming the sides of the ghat: it is from this conglomerate in such places consisting usually of a loose texture that the very excellent roads (for mountainous passes) are naturally made by the draining streams, which are only periodical. The conglomerate consists of water-worn stones of all sizes, even boulders are not unfrequent, yet the wearing is such as occurs in courses now filling the beds of torrents. The conglomerate increases in density and adhesion towards Lalpoor, and in many places is exceedingly hard.
Whatever the country may have been previously, one might explain its present appearance by supposing it to have consisted of a tolerably level extent of conglomerate, with here and there a strip of soil in the lowest part of each portion, and that the elevation of the mountain ridges was of subsequent occurrence: this would account for the formation of the lower slopes, and the frequent isolation of small eminences of the same character as the neighbouring mountains. It will account for the appearance of the conglomerate in every ravine until the top of the culminating point is reached.
As the mountains were elevated, portions of conglomerate would be detached, and these resting again on all suitable places, would account for the existence of conglomerate on certain parts which are flatter than usual.
Whirlwinds are common about Cabul, commencing as soon as the sun has attained a certain degree of power.
In all cases they assume the shape of a cone, the point of which being a tangent on the earth’s surface: the cone varies in shape, is generally of a good diameter, occasionally much pulled out, some being 2,300 feet in height, the currents are most violent at the apex.