Page:Popular Science Monthly Volume 38.djvu/443

Rh is much shortened. With the increase in the amount of fruit, according to Prof. Arthur, there is also a corresponding decrease in the size of the vegetative parts of the plant—that is, the stems and foliage. A tomato plant grown from green seed in the fourth generation was found to bear three and a fourth times as much fruit as top or stems and leaves together, while a similar plant from ripe seed had only one and an eighth times as much fruit as tops. It follows that, while earliness may be considered as a usual condition in all crops from unripe seed, an increase in the amount of the crop occurs only when the true fruit is the part harvested, as in tomatoes and peas, and a decrease in the amount of the crop occurs when any part besides the fruit is harvested, as in turnips and potatoes.

Imitative Coloring of Animals and Plants.—Among the later papers by Mr. Proctor in "Knowledge" is a study of color-mimicry in animals and flowers. It was suggested by observing a chameleon among the green leaves of an ivy, where it was as green as they. A fly of nearly similar color came along, and was instantly caught by the animal's nimble tongue. Afterward the chameleon settled on one of the sticks supporting the ivy, "and there it gradually assumed the same color, so far harmonizing with the stick that he seemed only an excrescence upon it, not a live creature which a short time before had been light green in color." This incident suggests some other illustrations of various forms in which color affects the development of life. Consider, continues Mr. Proctor, the striped tiger as an example of color in an animal that lives by preying on others, and the zebra as an example of color in an animal whose life depends on its not becoming the prey of carnivorous animals. "We can understand how, in certain regions, those members of feline races who chanced to have markings on their bodies which corresponded in appearance with the stems of trees, or with jungle reeds, and the like, would be better able to remain concealed till the animals which formed their prey came within certain range of their spring, and so would have the best chances of living"; and in like manner it is manifestly to the advantage of the zebra, when sleeping in the shade of trees, "to have markings on his body which from a distance would be confounded with the stems of trees and shrubs, beneath which for a while his active limbs were at rest. For so would he best escape the attacks of animals of prey. It is noteworthy that, when the zebra is stretched on the ground, the stripes on his legs as well as those on his body are vertical as seen from a distance. The same is the case in the tiger's stripes when the animal is couched for a spring." Another topic for speculation is the persistency of these imitative characteristics, which often appear as sports in the descendants of these animals ages after the purpose of their adaptation has ceased to exist. The author's attention was directed, while he was writing, to a sandy-colored cat "marked with stripes such as hundreds of thousands of years ago were of value to its remote ancestors in the struggle for life"; and a mule plowing in a field near his house had rings around his legs precisely corresponding to rings on the same parts in the zebra. In the vegetable world, color seems to be in all cases dependent on the requirements of propagation. Thus, where seeds are diffused by animals, as with the berries, we find the fruits brightly colored, to attract the attention of the animal distributors. It will be noticed that, when seeds are distributed by the winds, bright colors are not found in the fruit, even though the plant be closely allied to species distributed by animals in which the bright colors are present.

Bristling with Fire.—Photographic pictures of the smoke issuing from the mouth of a cannon at the moment it is fired show thin trails of fire about the circumference of the smoke-cloud, which give its edge the appearance of a porcupine's back bristling with quills. The trails are caused by the ignition of cubes of the pebble-powder which have been shot from the gun before the combustion was completed. Prof. W. Mattieu Williams has found, by examining the papers of Count Rumford, that he made experiments on the same subject, from which he inferred that in the ordinary firing of gunpowder in firearms the explosion must be gradual. In using powder in grains and cubes of sizes proportioned to the caliber of their guns, modern artillerists are only