Page:Popular Science Monthly Volume 19.djvu/735

Rh brought on by their habits of living. Bakers, tailors, and milliners are liable to consumption; compositors peculiarly so. Pressmen fare better than compositors, probably because their work is more active. In the country, farming appears to be the most healthy of occupations, while that of the innkeeper is the most fatal. Butchers die comparatively early, as also do brewers, draymen, and generally those who have much to do with establishments for eating and drinking. The over-exertion of those who follow athletic pursuits appears to conduce quite as much to short life as does the sedentary strain of the student. It seems to make but little difference in the "expectation of life" of in-door workers whether their labor is hard or not; but those who are employed out-of-doors have a chance of living six years longer, if their work keeps them busy and active, than if it is a mere matter of routine and standing around; and a "comparison of the tables leads us to the conclusion that the life of the out-door worker with little exercise is worse than that of the sedentary in-door worker, whether with little or with great exercise." The most curious fact brought out is that the scavengers, dustmen, and cleaners of sewers in London are reckoned among the healthiest of the population.

Conditions of Color in Flowers. The physiological processes of the coloring of flowers and the relations of different agencies, as light, temperature, the nature of the soil, and natural selection, are examined by F. Hildebrand in a work on the present variations and former development of the colors of flowers. The variations in the colors of flowers seem to be without limit, yet they are controlled by laws both in nature and in cultivation. Each kind has certain directions in which variations are more likely to take place, which are limited in extent, and are denoted by the colors which its congeners prefer. The character of the variations which any one species will take corresponds with the variation direction of other species of the genus, and can not be essentially changed by cultivation. All colors may be made to turn to white. Blue-blooming species may be made to vary to violet and red, but not, with the single exception of the blue hyacinth, to yellow. The variations of red-blooming species incline toward the colors of the nearest related species; if both yellow and blue kinds occur among the latter, the inclination is rather to the yellow tints, but a pure blue is never reached. Efforts have been made without success to produce blue pinks, zinnias, roses, hollyhocks, ranunculuses, primroses, and balsams. A yellow-blooming species will not vary to clear blue, even when there is a blue species in the same genus. Generally, the yellow-varying species belong to such genera as move in the red and yellow circle of colors, and the variations occur inside of this circle. The membrane of the plant-cells is nearly colorless. Colors arise either from the chlorophyl, the coloring-matter connected with the solid bodies within the cells, or through the coloring of the cell-juices, or by changes taking place in both the chlorophyl and the cell-juices. The red and orange colors are generally derived from the chlorophyl, as is exemplified by the fact that the red and orange masses in many flowers are frequently developed out of masses that were before green. The chorophylchlorophyl [sic] is seldom replaced by a red or blue grainy matter. White is readily produced, for all that it requires is the absence of chlorophyl or its presence in only a limited quantity. Other colors are produced by the coloring of the cell-juices with other matter than chlorophyl. So originate the rose-red flowers, some of the fiery red, most of the violet and blue. If no coloring takes place, the flower is white; hence the abundance of white flowers, and their occurrence whenever a species is made to vary. If a change takes place in both parts, if the chlorophyl is modified and the cell-juice is colored too, mixed colors, both bright and dark or dusky ones, are produced. A bright red often becomes prominent in this way, which, when combined with yellow arising from the chlorophyl, gives such colors as we find in the canna and nasturtium. Dark colors are produced by the association of green or yellow grains of chlorophyl with a violet juice, as in the nightshade. We look for the origin of diversities of color to conditions of light, temperature, and soil, and to the operation of natural selection.