Page:Popular Science Monthly Volume 8.djvu/522

506 of Montana, Wyoming, and British America. Prof. Cyrus Thomas, who has had an excellent opportunity of studying it—through his connection with Hayden's geological survey of the Territories—reports it as occurring from Texas to British America, and from the Mississippi (more correctly speaking, the line I have indicated) westward to the Sierra Nevada range. But in all this vast extent of country, and especially in the more southern latitudes, there is every reason to believe that it breeds only on the higher mountain elevations, where the atmosphere is very dry and attenuated, and the soil seldom, if ever, gets soaked with moisture. . ..

"My own belief is, that the insect is at home in the greater altitudes of Utah, Idaho, Colorado, Wyoming, Montana, Northwest Dakota, and British America. It breeds in all this region, but particularly on the vast hot and dry plains and plateaus of the last-named Territories, and on the plains west of the mountains; its range being bounded, perhaps, on the east by that of the buffalo-grass.

"In all this immense stretch of country, as is well known, there are vast tracts of barren, almost desert land, while other tracts, for hundreds of miles, bear only a scanty vegetation, the short buffalo-grass of the more fertile prairies giving way, now to a more luxurious vegetation along the water-courses, now to the sage-bush and a few cacti. Another physical peculiarity is found in the fact that while the spring on these immense plains often opens as early, even away up into British America, as it does with us in the latitude of St. Louis, yet the vegetation is often dried and actually burned out before the first of July, so that not a green thing is to be found. Our Rocky Mountain locust, therefore, hatching out in untold myriads in the hot sandy plains, five or six thousand feet above the sea-level, will often perish in immense numbers if the scant vegetation of its native home dries up before it acquires wings; but if the season is propitious, and the insect becomes fledged before its food-supply is exhausted, the newly-acquired wings prove its salvation. . . . Prompted by that most exigent law of hunger—spurred on for very life—it rises in immense clouds in the air to seek for fresh pastures where it may stay its ravenous appetite. Borne along by the prevailing winds that sweep over these immense treeless plains from the northwest, often at the rate of fifty or sixty miles an hour, the darkening locust-clouds are soon carried into the more moist and fertile country to the southeast, where, with sharpened appetites, they fall upon the crops like a plague and a blight. . . . The hotter and drier the season, and the greater the extent of the drought, the earlier will they be prompted to migrate, and the farther will they push on to the east and south.

"The comparatively sudden change from the attenuated and dry atmosphere of five to eight thousand feet or more above the sea-level to the more humid and dense atmosphere of one thousand feet above that level, does not agree with them. The first generation hatched in this low country is unhealthy, and the few that attain maturity do not breed, but become intestate and 'go to the dogs.' At least, such is the case in our own State, and in the whole of the Mississippi Valley proper. . . ."

Temperature and Vegetation in Different Latitudes.—A communication on this subject was made by M. Alphonse de Candolle to the Academy of Sciences of Paris, and reported in the Comptes Rendus for June 7th. The object of the inquiry was to test the accuracy of the very common observation that vegetation comes forward much more rapidly in spring in northern latitudes than in the warmer regions of the temperate zone. Experimenting with seeds of several species of plants sent to him from Northern and Southern Europe, he found that those from the north were most precocious. Twigs, obtained in the winter, of the white poplar, tulip-tree, catalpa, and the Carpinus betulus, from Montpellier, were there tried with twigs from the same species at Geneva. They were laid aside, so that their temperature might become alike, and were then placed in water, a little sand being put in the bottom of the jar.

The German, or more northern branches, leafed out first; the difference of time between the leafing of the respective pairs being from eighteen to twenty-three days.

It is an interesting question, "Why do northern plants develop more rapidly than southern ones?" Prof. de Candolle comments on it in this wise: "The buds of a tree are in a continual struggle. The later, like badly-placed ones, develop imperfect branches which are oftener stifled. The most precocious prevail, unless indeed they suffer from frost. In this way comes a selection, and a successive adaptation of the tree to the climate."

Buds, by this means, acquire peculiarities which are persistent. If there be promptness and quickness of growth, these qualities are continually reproduced. An instance of the persistency of acquired peculiarities is given in a horse-chestnut tree near Geneva, which, on a single branch, produced double flowers about the year 1822, and has continued to do so; and all the doubled-flowered horse-chestnuts in the