MASDEVALLIA. 21. 



level is nearly fifteen pounds to the square inch, or equal to that of 

 a column of mercury 30 inches high ; l)ut at 12,000 feet above sea- 

 level, an altitude reached by several of the jNIasdevallias, the pressure 

 is reduced to onedialf, or to about 7h pounds to the square inch, 

 and the mercurial cohimn of the barometer stands no higher than 15 

 inches. By repeated observations the mean annual temperature at sea- 

 level at the equator, and deviating but little from it for several 

 degrees of latitude on either side, is found to be 27 '5° C. 

 (82° F.), but at an elevation of 12,000 feet in the same latitude 

 it is only 7° C (45° F.). At this elevation on the Andes of Peru, 

 it has been observed that on clear days, the mean temperature at from 

 one o'clock to three p.m. is nearly doubled, and at night tire 

 thermometer sinks to near the freezing point The atmosphere is, 

 however, constantly charged with moisture, caused by the vapours 

 rising from the hot plains drenched by the e(piatorial rains on the 

 eastern side of the mountains, and which are drifted thither by 

 aerial currents, or attracted by the mountains themselves. In New 

 Granada the climatic conditions of the Odontoglossum and Masdevallia 

 zone are not very different from those of Peru, except that in 

 consequence of the loAver elevation, the atmospheric pressure is greater, 

 and the mean temperature somewhat higher. Here on clear days the 

 direct rayd of a tropical sun cause oppressive heat, while its rapid 

 radiation into space at night produces chilling cold ; but both extremes 

 are constantly being modified by the humidity of the atmosphere, 

 scarcely a day passing on which this, at one time or other, is not at 

 the saturation point. At Sonson, rain is frequent ; almost every morning 

 there is a dense fog, and on the neighbouring heights the temperature 

 not infrequently sinks below zero ('52" F.).* Generally, on the Cordilleras 

 of New Granada and Venezuela, the rainy season lasts throughout the 

 greater part of the year, owing to the immense quantity of aqueous 

 vapour raised from the Atlantic Ocean being constantly blown towards 

 them by the north-east trade wind. 



Cultural Note.— The Masdevallias are usually cultivated in the ""cool'' 

 house with Odontoglots, Oncids, etc , but where they are matle a 

 speciality hj amateurs or grown on a large scale by horticulturists, a 

 separate house is assigned to them, in which they can be more 

 efficiently treated according to their requirements, than when mixed 

 with plants of other genera. When a separate house is so devoted to 

 them, a lean-to with an east or north-east aspect should be preferred. 



On their native mountains, the Masdevallias grow in a variety of 

 situations — on the ground, in the crevices of rocks, on the trunks and 

 branches of trees, and even on the roofs of buildings, but always where 

 there is but little or no soil, or where there is but a small accunudation of 



* Roezl in Godefroy's OrcMdojjhile, 1883, p. 643. 



