Fig. 7. and 8. c, The roots in the procumbent species, issuing from the cellular substance, and descending into the soil, from the under side of the stein, opposite the ger minating buds. Each of these shoots, therefore, when de tached; from so many distinct plants, possessing the full diameter of the adult stem, and, like those mentioned by KRinpfer, occasionally shooting in the same manner, from the stem of palms, attain speedily their perfect form. It was, I believe, Michell who first described the calyptres or covers on the extremities of the roots in certain aquatic. plants. Sprengel has observed these covers on the extre mities of the fibrous roots of ferns, and supposes them to be organs of absorption, in some degree analogous with the ampullm in the villous coat of the intestinal canal of animals. To us, it would seem probable, however, that these covers, like the chaffy scales of the stems and fronds, are intended rather to protect the delicate extremities of the absorbent roots, than to perform this office themselves.
THE buds from which the frolic's of these plants are evolved, form part of the great central tuber from which the stem itself is produced. This tuber, in our northern climate, is found during winter, surrounded with'the decay ed stipites of the fronds of the preceding season, and close ly invested with the woolly scales already mentioned. In examining these buds separately, we find that it is the su perior part or frond only which is involute, or circinate, as it is termed the stipes itself being extended nearly in a straight line from its origin within the stem. In the ?911i dium fzlix alas, we have traced the diverging vascular fas ciculi within the stem, before the external developement of the fronds ; and this appears evident in some species on cutting it across, when the large central fasciculi of the stem appear surrounded with the smaller ones of the sti pites of former years, (Fig. 7. d). The reason these are not perceptible in the section of the stein, represented in Fig. 8. ut supra, is, because it is difficult to recognize them in tilt young succulent stein, as distinct from the cellular substance. The term lignum fasciculation, used by Dau benton and Desfontaines to designate the stems of monocoty ledonous plants, is in fact peculiarly applicable to the ma ture Item of ferns. For these fasciculi may be seen even by the naked eye, and traced from their first divergence within the stem, to their final termination in the as they are termed, of the frond, in many instances in contact with the groups of capsules.
Sprengel had the merit of first pointing out this circum stance ; and he supposes " the vascular fasciculi contain j the concentrated sap, analogous with the proper juice of other plants, which is elaborated in the thick solid tubers of ferns, from the humidity of the earth absorbed by the roots. The oxygen of the carbonated water entering the loose cellular texture, while the carbon, uniting with the hydrogen, is conveyed into the ascending spiral vessels, where it contributes to the formation of the fruit, while the brown membrane surrounding the fasciculi, prevents the admixture of the elaborated sap with the crude juice of the cellular texture.—This construction," he adds, " throws light on the peculiar origin of the seed-vessels m I hese plants, which takes place immediately from the ribs of the frond, of the continuation of the spiral vessels." It is very probable, that the vascular fasciculi pellet m an important office in the formation of the parts of fructifica tion in ferns; but it is equally so, that the fronds, like time leaves of other plants, contribute their part in the assimi lation of the saccharine mucilage contained in the cellular substance of the stem, which would seem destined, not on ly to the nutrition and evolution of the infant germs inva riably imbedded in it, but to the developement of the fruit itself. What renders this opinion more probable, is the circumstance, that the abundance of the saccharine matter increases or diminishes with the health or weakness of the respective plants, and in the autumn after the ripening of the seeds, it is exhausted, and the cellular matter itself partly disappears, and the central part of the stipites is found hollow. However, an abundant supply is deposited in the stem for the use of the buds the following season. In short, this saccharine mucilage seems to possess a remark able analogy with the cambium of Duharnel, from which, in other plants, both buds and seeds are apparently develo ped, and subsequently nourished and perfected.
Although in by far the greater number of species the buds are produced from the stern, there are many others, as Polypodium reptans, in which buds are evolved from the top of the frond. Indeed in their general structure, the stipites of the fronds possess a considerable analogy with the branches of other plants ; but they also combine with this the properties of leaf and fruit-stalks. There are however, some species, as Schiz ea dichotoma of Smith, and S. bifida of Willdenow, whose stipites are destitute of fronciose expansions.