. The theory of horticulture. some leaves ofMint (Mentha piperita), without any portion of thesubstance of the stems upon which they had grown,were planted in small pots, and subjected to artificialheat, under glass. They emitted roots, and livedmore than twelve months, having assumed nearly thecharacter of the leaves of evergreen trees; and uponthe mould being turned out of the pots, it was foundto be everywhere surrounded by just such an inter-woven mass of roots as would have been emitted byperfect plants of the same species. These roots pre-sented the usual character of those organ?, and c
. The theory of horticulture. some leaves ofMint (Mentha piperita), without any portion of thesubstance of the stems upon which they had grown,were planted in small pots, and subjected to artificialheat, under glass. They emitted roots, and livedmore than twelve months, having assumed nearly thecharacter of the leaves of evergreen trees; and uponthe mould being turned out of the pots, it was foundto be everywhere surrounded by just such an inter-woven mass of roots as would have been emitted byperfect plants of the same species. These roots pre-sented the usual character of those organ?, and con- OF PROPAGATION BY LEAVES. 193 sisted of medulla, alburnum, bark, and epidermis;and as the leaf itself, during the growth of these, in-creased greatly in weight, the evidence that it gene-rated the true sap which was expended in their for-mation appears perfectly conclusive. In our gardens, we know of many other cases ofthe same kind. Hoya is a common instance, and threeothers are here figured {fig. 18); viz., Gesnera (a),. 194 APPLICATION OF PRINCIPLES. Clianthus puniceus (6), Gloxinia speciosa (c). In these,and all such cases, the first thing that happens is anexcessive development of the cellular tissue, whichforms a large convex callus at the base; fromwhich, after a time, roots proceed; and by whicheventually a leaf-bud, the commencement of a newstem, is generated. It is not surprising that leaves should possess thisquality, when we remember that every leaf does thesame thing naturally while attached to the plant thatbears it; that is to say, forms at its base a bud whichis constantly axillary to itself. Leaves, however,have not been often employed as the means of pro-pagating a species; and it is probable that mostleaves, when separated from their parent, are incapa-ble of doing so, for reasons which we are not as yetable to explain. The most common case of their em-ployment is in the form of the scales of a bulb, whichwill, with some certainty, produce new plants unde
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