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Page:Popular Science Monthly Volume 61.djvu/490

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two miles long and two or three hundred yards wide, and over a still smaller area a little farther south. The California fan-palm only occurs in a few canyons of two mountain ranges in the southern part of the state. The western hop hornbeam is only known to grow over a few square rods of territory in the Grand Canyon of the Colorado river in Northern Arizona. In eastern United States, Torreya only grows in a narrow strip on the eastern bank of the Appalachicola River in Florida: while the Florida yew, which grows in the same region, occupies a still less extended area.

In such cases as these it is likely that the structural and physiological adaptions of the different plant organs have not kept pace with the natural changes in environment. As a result, these trees are not only unable to extend their present range, but are poorly fitted to persist where they now grow and consequently are disappearing. These old types of trees have in the course of ages become inflexible and fixed and are no longer in perfect accord with their environment. More modern types, as illustrated in the various genera of Cactaceae, are more generalized and very readily take on structural and physiological modifications which fit them better to their present environment. It is interesting to note that many of the species which appear to be out of accord with their natural environment often do well under cultivation. The gardener's care in subjecting them to different environmental conditions, particularly as regards food supply, seems to stimulate them and give them new vitality, thus causing them to succeed better than more modern types perfectly in accord with their natural environment. In the latter case overstimulation, induced by cultivation, may from the standpoint of vitality do more harm than good.

The Monterey cypress, although now nearly extinct as a wild plant, is one of the most successful and easily cultivated trees of the Southwest. It appears to be far better in accord with the artificial environment induced by cultivation than it is with its natural environment. The Franklinia of our gardens, a small tree first collected by John Bartram in 1765 on the banks of the Altamaha River in Georgia, is successful in cultivation, although as a wild plant it passed out of existence during the past century. It is far more successful in cultivation than the Loblolly bay, an allied species of the same genus which is now growing wild from Virginia to Florida. The Ginkgo, an Asiatic tree of ancient origin, grows remarkably well in cultivation, although at the present time it is not known to grow as a wild plant any where.

Modern plant types that have not yet reached the limits of their distribution and variation, as illustrated in many species of the Compositae, Rosaceae and Cactaceae, are so nicely adjusted to their natural environment that cultivation often tends to diminish their vitality rather than improve it.