Page:Popular Science Monthly Volume 50.djvu/190

176 purposes and usefulness of these institutions have steadily broadened until all the more important phases of the subject are more or less represented in the greater majority of instances.

In addition to the scientific and practical uses enumerated above, the botanic garden has become a laboratory for the landscape artist, who may dispose of its masses of plants with a feeling regard for their artistic value in outline and color, making a most effective means of cultivation and gratification of public taste. In many of the better known gardens, especially those located in the great cities, this æsthetic feature has become a very prominent and in many instances the predominant idea.

Only when a botanic garden is equipped with laboratories for the furtherance of investigation, and sustains an organic relation to a school or university, may it be said to attain its highest possibilities of usefulness, in the demonstration of the principles governing the nature and development of one of the two great groups of living things. When designed for this purpose the collection of growing plants should represent as many of the principal forms of vegetation as is possible. Since the probable number of living plants is estimated at half a million, it is obviously impossible to bring together in any restricted area more than a fraction of this number. A census of the flora of the section of Bronx Park in New York, inclusive of about two hundred and fifty acres, which is to be converted into a botanic garden, showed that nearly a thousand species of ferns and seed-forming plants were to be found on that area, only a small number of which were introduced. Of these thousand species many were represented by thousands or perhaps hundreds of thousands of individuals. In the conversion of the tract into a botanic garden, the gardener will remove all but a few dozen, or perhaps a few hundreds, of each species, which will be confined to certain designated limited areas. In this way he will relieve each species from the competition of its neighbors, and so far as possible from the ravages of insects and animals—the most telling factors in the struggle for existence—and obtain space for the introduction of a large number of species. If these conditions alone determined the flora of a region, the number of species which could be grown in a garden would be determined only by its size and the number of plots it might contain. It is found, however, that the substratum and climate offer rigid limitations to an extension of the flora which may be grown out of doors in any locality. The gardener partially overcomes this limitation by the use of glass houses, where plants from nearly all parts of the world may be grown in specially prepared soils, and kept at temperatures resembling those of the natural habitats of the plants. But under such conditions it becomes extremely difficult to properly adjust the moisture and