Page:Popular Science Monthly Volume 27.djvu/440

424 of heat. 'Mr. Wallace, defending his view, says that, "if the white coloration of the Arctic animals stood alone, it might be thought necessary to supplement the protective theory by some physical explanation, but we have to take account of the parallel cases of the sand-colored desert animals, and the green-colored denizens of the ever verdant tropical forests; and, though in both these regions there are numerous exceptional cases, we can almost always see the reason of these, either in the absence of the need of protection, or in the greater importance of conspicuous covering. In the Arctic regions the exceptions are particularly instructive, because in almost every case the reason of them is obvious." The Arctic wolf does not turn white, because he hunts in packs, and concealment is not necessary; the musk-sheep, yak, moose, caribou, and reindeer are able to take care of themselves, and need no protection or concealment. The glutton and sable are dark colored because they live in trees, and must look like them. The raven, living on carrion, requires no concealment, and continues black. Mr. Wallace is of the opinion that color has very little to do with the absorption or radiation of heat, because those matters are largely determined by the structure and surface-texture of the colored substances.

A Mystery of the Growth of Trees explained.—Mr. John T. Campbell relates in the "American Naturalist" his discovery of one of the causes of the phenomenon of particular tracts of land being covered with a simultaneous, nearly exclusive, growth of trees of a particular species. Some have ascribed the phenomenon to a peculiar fitness of the soil to particular kinds of vegetation, which he does not find to exist. His own explanation is very simple, and is to the effect that the matter lies wholly or mainly in the fact of the ground being in a fit condition to receive the seeds of the various species when they fall upon it. Seeds of different kinds fall at various seasons, and when the ground is in various conditions as to moisture, etc. Those that find the ground in good condition sprout and grow, if no accident occurs to remove the plants when very young. Mr. Campbell has tested this view in his surveys in the occasionally flooded bottom-lands of the Wabash River, and illustrates it by following the futures of the seeds of three species of trees. The balls of the sycamore or button-wood begin falling early in the spring months, and, if a flood is receding at the time, they stick to the soft, moist banks wherever they touch them, and particularly along the highest parts of the sand-bars. Were it not for the subsequent floods in the same spring, no other trees could grow, for these would occupy the ground. But they are easily killed during their infancy by overflows, and this is what happens to most of them. The Cottonwood is the next in order of shedding seed, and, if another flood is receding while this is taking place, it will have killed all the sycamores which it has covered, and sprout the cottonwoods. These in turn may be killed by the next flood. It is the turn of the maples next to shed their seed, and try for the ground. If either of these species succeeds in making wood without a flood, it will hold the ground, and its rivals will not be able to get a place. Last spring the edges of the successive plantations escaped the next floods after the seeds fell upon them, and Mr. Campbell could see along the river-banks three belts of young trees, and distinguish them by their general appearance. The upper belt was of sycamore, the second (downward) of Cottonwood, and the third of soft maple. In June a bigger flood came than any that caused the seeds to sprout, and killed all the young trees.

Water-Melon Sirup.—In response to the inquiry by Dr. H. Carrington Bolton concerning the manufacture of sugar from water-melons (see June number, page 287), Mr. E. A. Gastman, of Decatur, Illinois, writes as follows: "About 1842 the manufacture of molasses was carried on here in Central Illinois from melons. I do not know how extensive nor how successful it was, but I remember very clearly when a boy on the prairies near Bloomington that our neighbors frequently raised large crops of watermelons, from which they made molasses." It will be observed that the extract from Boyle's work communicated by Dr. Bolton mentions a "sirup," not sugar.