At the time (1864) when this Monograph was commenced, the successful application of the system of cool treatment to Orchids accustomed to a moderate temperature in their native haunts gave a fresh impulse to the cultivation of that charming tribe of plants. By its means, what might almost be regarded as a new Orchid-world, teeming with interest and beauty, was suddenly brought within our reach. A fresh field was opened to the enterprise of collectors, the spirits of cultivators revived, and the hopes of botanists mounted high. Foremost among the spoils that we sought to secure, stood the various members of the genus Odontoglossum, which from the days of Humboldt and Lexarza, was known to abound in species pre-eminent for the loveliness and delicacy of their flowers but which had hitherto mocked the utmost efforts of our most skilful growers. For although (thanks to the labours of Warczewitz and Lobb) the Horticultural Society and Messrs. Veitch had more than once received large consignments of Orchids