Odontoglossum.—The Odontoglossums are deservedly the most extensively grown genus of cool-house Orchids, the larger proportion of those in gardens being represented by O. crispum (illustrated in [Plate VIII].), one of the most beautiful of Orchids. The spotted forms often realise very high prices. Cool, moist houses are provided for O. crispum and its section of Odontoglossum; in some gardens several houses are allotted to the species. Given a suitable house and careful treatment, the Odontoglossums are among the easiest Orchids to grow, and the most certain to flower. All the species generally classed with O. crispum should be grown in well-drained pots. The compost in which they are grown used to be formed exclusively of Orchid peat and Sphagnum-moss, and, where these materials can be obtained of good quality they have never been improved upon. There came a craze in some collections for putting the Odontoglossums in leaf-soil, which ended in disaster, although it indicated that a proportion of dry leaves (not leaf-soil) may be used in the compost with advantage. Scarcity of good Orchid peat brought about the introduction of Polypodium fibre and Osmunda fibre, both excellent materials when prepared as recommended in the chapters on Potting Epiphytal Orchids, and Hybrid Orchids. For the general repotting of those requiring it September is the best month, but in early spring the plants should be examined in order to repot those which need immediate attention. The Odontoglossum house must be kept cool at all seasons, and the necessity to have lower night temperatures must be strictly recognised. Free ventilation should be provided, but at all seasons when drying, east winds prevail, especially in winter and early spring, the bottom ventilators should be only opened slightly, the top ones being kept closed; the laps of the glass of the roof will admit sufficient air. Moisture should be freely distributed about the house by syringing beneath the staging and between the pots in summer, but in winter the houses, if kept at the prescribed low temperature, will be moist without much water being distributed. Odontoglossum citrosmum, O. Rossii, O. membranaceum, and some other Mexican species should be grown in baskets or pans; O. coronarium and its varieties in oblong baskets; O. Londesboroughianum on rafts. Odontoglossums require abundance of water, but are easily injured if allowed to get soddened. Water should therefore be given systematically—a thorough watering, and no more until the effect of it is passing and the still moist material is sufficiently near the dry point. After flowering, a lessened supply should also be given for a time, but the plants must not be dried off. At this stage it is a good time to repot any requiring to be repotted. In the cool houses, and indeed all the Orchid houses, observation should be made as to the rapidity of evaporation of water from the floors and staging. If the moisture evaporates too quickly and the floors and stages become dry rapidly, it must be remembered that the conditions are not favourable to sustaining the vitality of the plants in the house, for, where rapid evaporation takes place, a similar process affects the tissues of the plants. Means should be taken, either by lowering the temperature or checking the ventilation, to sustain a lasting humidity in the houses.
Oncidium.—This is a large genus, most of the members being suitable for cultivation in the intermediate house. O. macranthum is a cool-house plant, and O. crispum, O. Forbesii, O. concolor, O. Marshallianum (illustrated in [Plate VII].), O. varicosum, and others also do well in the cool house in baskets or suspended pans. O. Papilio, O. Kramerianum, O. Lanceanum, and O. ampliatum should have a position in the warmest end of the intermediate house. Pot the plants as epiphytal Orchids. Withhold water for a time after growth is completed.
Paphinia.—Small-growing epiphytes. Grow in baskets or pans in a warm, moist house.
PLATE VIII
ODONTOGLOSSUM CRISPUM
Phaius.—Strong-growing, terrestrial Orchids for the intermediate house. Pot them according to the directions in the chapter on the potting of terrestrial Orchids. The species are evergreen, and require but a short resting season. They require shade.
Phalænopsis.—These are warm-house species from the Philippines, Java, Borneo, India, and other places. Pot the plants in Sphagnum-moss. They succeed best when suspended, but if they are grown on the stage they should be elevated on inverted pots. A moist atmosphere is essential. P. amabilis Rimestadiana will grow in the intermediate house; so will also most of the other species, if placed in a moist corner.
Peristeria.—The genus is best known in gardens by P. elata (Dove Orchid). The cultivation is similar to that for Phaius.