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by him in the Annales des Sciences, n. s. x. 319. t. 3., from Marchantia polymorpha, Chara vulgaris, Sphagnum acutifolium, and Hypnum triquetrum.
M. Payen, in a second memoir upon this subject, names the unchanged primitive tissue of plants cellulose, and says it has the same composition as starch; the matter of lignification he regards as the true lignine of chemists. (Comptes rendus, viii. 52.)
The observations by Mr. Griffith on Indian Loranthaceæ have been continued by M. Decaisne upon the common Mistletoe ; and he finds that, although that plant flowers in the months of March and April, the ovule does not make its appearance earlier than the end of the month of May, or the commencement of June. (Comptes rendus, viii. 202.)
All these statements have now been copiously illustrated by excellent figures in Schleiden's memoir Ueber Bildung des Eichens, und Entstehung des Embryos bei den Phanerogamen.
There are some secondary forms under which nutritive matter is provided for plants, the most important of which is starch. The purpose which nature intends this almost universally diffused substance to answer, in the system of vegetation, is essentially nutritive. It is formed in plants soon after their parts become organised, and it collects there till in some instances, such as albumen, tubers, rhizomata, and the cellular part of endogenous stems, it forms the principal part of the mass. In such cases it is ready to be chemically changed at a fitting period, and to become the food of the germinating embryo, or of young stems and leaves. According to M. Payen, it is enabled to execute this important purpose, by virtue of its gradual solution by water and diastase, which convert it into dextrine and sugar, and thus render it capable of percolating the surrounding tissue, and passing from chamber to chamber of parenchyma. (Mémoire sur l'Amidon, p. 131.)
According to Payen (Comptes rendus, viii. 60.), those manures are the most efficient which are richest in nitrogen, for he considers that plants are generally able to obtain, in most cultivated soils, a sufficient supply of the other principles necessary to their existence, without the addition of manure. But this does not quite agree with an assertion of Boussingault, that although some plants rob the air of a considerable quantity of nitrogen, yet others do not assimilate it at all. (Ib. 55.)
Mr. Rigg has investigated the connection between nitrogen and plants, the results of his enquiries being given in the Philosophical Transactions for 1838, p. 395. &c. He finds the youngest parts of plants richest in nitrogen, the germ of Peas and Beans containing by weight about 200 parts of that gas for 1000 parts of carbon, while the cotyledons contain only from about 100 to 140 parts. He is disposed to believe that those seeds of the same kind, which contain the largest quantity of nitrogen, germinate the earliest. Alburnum he finds to contain more nitrogen than duramen, and fast-growing timber more than slow-growing, whence he infers that nitrogen exercises its influence in causing decomposition. The latter opinions he considers to be rendered still more probable by the proportion of nitrogen found in different species of wood, cæteris paribus: thus in satin wood and Malabar teak, both timber of great durability, the quantity of nitrogen is almost inappreciable; in Dantzic and English oak, the quantity is also very small; in American birch which soon decomposes, nitrogen is found in large quantities. Mr. Rigg finds nitrogen in large quantities in Vine leaves when they first make their appearance: as they are developed it decreases in proportional quantity; is in excess during the period of most rapid growth, and towards the close of the year it is comparatively small. He states the full-blown petals of the Rose to contain 24 parts of nitrogen in 1000 of carbon, while the unexpanded and central petals contain 66 parts.
In another paper also published in the Philosophical Transactions for 1838, p. 403., Mr. Rigg has considered the evolution of nitrogen during the growth of plants, and the sources from which they derive that element. He states that his enquiries all tend to prove that nitrogen is evolved during the healthy performance of the functions of plants; that the proportion which it bears
to the oxygen given off is influenced by the sun's rays; but that owing to the necessary exclusion of the external atmosphere during the progress of experiments, it is impossible, with any degree of accuracy, to calculate the volume of these evolved gases during any period of the growth of plants in their natural state. If to this indefinite quantity of nitrogen given off by plants, there be added that definite volume incorporated into their substance, the question arises, whence do plants derive their nitrogen, and does any part of it proceed from the atmosphere? This problem Mr. Rigg has endeavoured to solve by a series of tabulated experiments upon seeds and seedling plants, the result of which is a large excess of nitrogen in the latter, and under such circumstances of growth that he is compelled to fix upon the atmosphere as its source. He has also arrived at the conclusion, that the differences which we find in the germination of seeds and the growth of plants in the shade and sunshine, are due in a great measure to the influence of nitrogen.
EXPLANATION OF THE PLATES.
N. B. All the figures in the plates. of which the following is an explanation, are more or less magnified: the drawings from which they have been prepared are in all cases original, except where it is stated to the contrary.
Fig. 1. A small portion of a section of the cellular tissue of the pith of Calycanthus floridus, showing the pore-like spots upon the membrane, Fig. 2. A section of the leaf of Lilium candidum; after A. Brongniart: a, epidermis of the upper surface; b, ditto of the lower surface; c, stomata cut through in different directions; these last are seen to open into cavities in the parenchyma; d, upper layer of parenchyma; e, intermediate ditto; f, lower ditto. Fig. 3. Cubical cellular tissue, passing gradually into prismatical, from the stem
of the gourd, cut vertically; after Kieser.
Fig. 4. Fibres forming arches in the endothecium of Linaria Cymbalaria; after Purkinje.
Fig. 5. Fusiform cellules in the wood of a young branch of Viscum album; after Kieser: a, common hexagonal cells of the pith, with grains of amydon sticking to their sides; b, fusiform cellules, considered by Kieser to be pierced with holes; c, other cells of the same figure, with lines of dots spirally arranged on the membrane; d, others, in which the dots are run into lines; e, f, others, in which the cellules have all the appearance of short spiral vessels. Kieser considers these not as spiral vessels, but as cellules of a peculiar kind, replacing spiral vessels in the Viscum.
Fig. 6. A portion of the cuticle of Billbergia amoena, with the membrane torn on one side, showing that it does not tear with an even edge, but breaks into little teeth.
Fig. 7. Muriform cellular tissue, forming the medullary processes of Platanus occidentalis. Each cellule contains particles of brownish matter of very irregular size and form.
Fig. 8. a, Glandular hairs of the peduncle of Primula sinensis; 1. the glandular apex more highly magnified, with a particle of the viscid secretion of the species on its point; 2, the apex of another hair, showing that the end is open, a conical piece of the viscid secretion lying in the orifice; b, a hair of Dorstenia, showing the cellular base from which it arises, and that it consists of a single hollow conical curved cell.
Fig. 9. A branched hair from the cilia of the leaf of a species of Verbascum. Fig. A. A simple coloured hair in Dichorizandra rufa.
Fig. B. A hair with tumid articulations from the leaf of Gesneria tuberosa.