For mixing with the compost for hybrid Orchids, some use crushed crocks, sand, charcoal, and a small proportion of each or either may be employed safely, although there is no real need for such materials.
Polypodium fibre may also be substituted for Osmunda fibre, or a proportion of each may be used. Orchid peat fibre, which used to be the chief potting material for Orchids, is still perhaps as good as any of the other fibres, provided a really good quality can be obtained, a matter which has become increasingly difficult.
For Cypripediums, and especially Selenipediums, a proportion of good, fibrous loam should be added to the compost recommended for epiphytal Orchids, the proportion of loam being increased as the plants get larger. Phaius, Calanthes, Zygopetalums, Zygocolax, and other plants of a similar character should also have a proportion of loam-fibre in the compost, and in these cases Orchid peat may be substituted for Osmunda fibre, if it is of good quality. So far as it has been tested, Osmunda fibre has an advantage over other fibres, in that it is more durable, retaining its fibre intact longer than any other. Osmunda fibre and Polypodium fibre in equal proportions, with an addition of leaves and Sphagnum-moss, make an excellent material for all young, epiphytal Orchids, the finer Polypodium fibre, if well worked in, giving substance to the more open Osmunda fibre.
For very small plants it is well to rub the mixture through a coarse sieve, but after the early stages the use of the sieve should be discontinued, and the compost carefully mixed with the hands.
CHAPTER XX
ENUMERATION OF THE PRINCIPAL GENERA AND SPECIES IN CULTIVATION
Acanthophippium.—A small genus of terrestrial plants with oblong pseudo-bulbs, and broad, plicate leaves. Scape erect, flowers ventricose, yellow and reddish-purple. Warm house. Pot in equal parts of turfy loam, peat, and leaves. Rest dry after the leaves fade and growth is completed. The most familiar species are A. bicolor, A. javanicum, and A. striatum.
Acineta.—The species of Acineta are epiphytal Orchids with stout pseudo-bulbs and broad, coriaceous leaves. The flowers are produced in pendulous racemes; they are fleshy, whitish, or yellow, and spotted with purple or brown. They should be grown in baskets suspended in the intermediate house. A. Barkeri, A. densa, and A. Humboldtii are free-growing species.
Acropera. See Gongora.