Page:Popular Science Monthly Volume 50.djvu/335

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319
BOTANIC GARDENS.

ecological and æsthetic requirements. A small portion is devoted to aquatic plants, a second to an arboretum, another to anexperimental plot inclosed and accessible only to workers. In the entire garden the instinctive ability of the naturalist is shown in the selection of natural conditions for the specimens of the various flora represented, and the alpinum may be regarded as a triumph in the art of artificial culture.

The alpinum is laid out in the northwestern part of the garden on a rectangular plot of ground one hundred and ninety feet in length and nine feet in width, near a stone wall seven feet high and parallel to its length. On this plot are piled the rocks and soil necessary for the culture of plants, in an uneven ridge, which in one place is six feet in height. The materials used were principally the native stalactite limestone and gravelly soil and granite from the Black Forest, forty miles distant. The limestone is peculiarly suitable for the lower Alpine plants and lithophytes, furnishing, as it does, innumerable cavities for the reception of soil and secure foothold for plants which cling directly to the rock. It has been found that the species from the higher European Alps refused to grow on such rock, and hence the granite was procured for the section devoted to this group. The entire structure is in many respects an admirable imitation of an east-to-west mountain ridge. The northern side affords many shaded crevices, and more or less shade to the whole is given by a number of small trees near by.

The most difficult problems which have confronted the gardener in the construction and management of the alpinum have been those connected with the water supply. The water content of such rocky soils is of course extremely small and needs almost constant replenishment. In Nature this is done by water from the melting snows above. Here it has been accomplished by a system of branching pipes with many openings below and above the surface, and a flow is allowed during the greater part of the day. The drainage is carried away by cement conduits, and in one place forms an Alpine lake eight feet in length and five feet in width, which furnishes in its waters and on the overhanging cliffs admirable conditions for a very rich flora. Near the lake are growing several specimens of Edelweiss, which here becomes somewhat longer stemmed than on its native cliffs, or in the Alpine gardens where it is cultivated to satisfy the thirst of the tourist for mementoes of "hazardous" ascents.

Many of the Alpine plants are quite intolerant of lime salts and grow best on the granite rocks, but the water supply used here is taken directly from the city system and is very richly charged with these substances, and as a consequence the culture of some of the plants of the higher slopes is impos-