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Cotyledon (a name used by Pliny, meaning a cavity, having reference to the concaved or cup-like leaves of some kinds). Crassulaceae. Succulent herbs or shrubs, rarely annual, grown mostly for their oddity, but some of them making good winter bloomers in pots and some used for summer bedding because of the stiff thick foliage; some are half-hardy North.
Habit very various, rosulate or erect, sometimes of a scandent tendency: branches and lvs. thick and fleshy: lvs. opposite or alternate, petiolate or sessile: calyx 5-parted, as long as or shorter than the corolla-tube; corolla tubular, cylindrical or urn-shaped, sometimes 5-angled, the parts or petals 5, erect or spreading, connate to the middle, longer than the usually 10 stamens; ovary of 5 free carpels, each with a narrow scale at base; fls. erect or pendent, sometimes showy, in terminal racemes or cymes. Differs from Sedum in the connate petals.—Species about 100, in Calif, to Texas, and Mex., Afr., Asia and Eu. See I.H. 10:76 for an account of many of the species. Some of the species make dense rosettes of stiff lvs. on the ground and send up a small bracted scape; they remind one of the house- leek (Sempervivum tectorum and related species).
As above defined, Cotyledon comprises the broad group habitually known under that name. Recently, however, Britton and Rose have revised the group, excluding Cotyledon from America, reinstating Echeveria and Pachyphytum for some of the American species and making new genera for others, as Dudleya, Oliveranthus, Urbinia, Stylophyllum. For the convenience of the gardener, the cult, species are here brought together under Cotyledon, and they are also listed at other places under their new generic names.
Cotyledons are little known in this country except among fanciers and for carpet-bedding. Culturally, there are two groups,—the greenhouse kinds and the bedding kinds. The greenhouse kinds are well represented by C. gibbiflora. It is attractive both in foliage and flower. It may be expected to begin bloom in January or February. Its period of bloom is short, after which it may be propagated. The top of the main shoot (or of strong side shoots) may be cut off with 2 or 3 inches of stem, and stood in pots so that the cut end will rest on moss in the bottom and the leaves on the rim of the pot; using no earth; fine roots will soon form and the young plant may then be repotted into dryish soil. The old stems of this and similar tall kinds may be placed rather close together in shallow boxes, when it is desired to propagate them, and kept in a warm dry place, where they will form small growths along the stems; these, when large enough, may be put into boxes of dry sand, and potted in thumb- or 3-inch pots when they have made a sufficient quantity of roots. This species should be kept in a warmhouse in winter, where it is rather dry and not exposed to drip. C. fulgens is a good greenhouse species, producing showy waxy red flowers in winter; also C. coccinea. For this purpose the large plants should be lifted from the beds and carefully potted, as they make a much finer growth in the open ground than when grown in pots. — When it is desired to increase the Tow-growing carpet-bedding kinds on a larger scale, the plants should be lifted before the ground gets too wet and cold. They may either be boxed in dry soil and kept in a cool dry house, or placed thickly together in a frame, taking care that no drip is allowed on the plants, and giving no water. The most convenient time for propagation by leaves is during the months of November and December, when the fall work of rooting soft-wooded plants is over. Leaves rooted at this time will make plants large enough for planting out the following season. They will take from three to four weeks to root, according to the kind. The leaves must be taken from the plant as follows: Grasp each leaf between the thumb and forefinger, give a gentle twist first to one side then to the other until the leaf comes off, taking care that the dormant bud in the axil of the leaf accompanies it, otherwise the leaf will root but a plant will not form from it. Make a depression about 2 inches deep in the center and 4 inches wide across the sand-bed, in this lay two rows of leaves with their bases touching each at the bottom of the depression; give no water until the small roots make their appearance, and only slightly afterwards. When the little plants are large enough they should be boxed, using sandy loam, and kept in a temperature of not less than 60° F. at night.—For summer bedding purposes the following have been employed very successfully, being lower growers: C. atropurpurea, C. fulgens, C. coccinea, C. fascicularis, C. gibbiflora var. metattica, C. Pachyphytum, C. Peacockii, C. Purpusii, C. roseata, C. secunda, C. secunda var. glauca, C. mexicana. (G. W. Oliver.)
Other species of Cotyledon occur in collections of succulent plants, but the following probably represent those of commerce in this country.
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[[Image:Seedling_cotyledons_small.jpg|thumb|right|This [[seedling]] germinated producing two plain-looking cotyledons later followed by two normal-looking leaves that are small copies of the adult leaves.]]
[[Image:Seedling_cotyledons_small.jpg|thumb|right|This [[seedling]] germinated producing two plain-looking cotyledons later followed by two normal-looking leaves that are small copies of the adult leaves.]]
[[Seed]]-[[leaf]]; the primary leaf or leaves in the embryo; in some plants the cotyledon always remains in the seed-coats and in others (as [[bean]]) it emerges on [[germination]].
[[Seed]]-[[leaf]]; the primary leaf or leaves in the embryo; in some plants the cotyledon always remains in the seed-coats and in others (as [[bean]]) it emerges on [[germination]].