THE POPULAR SCIENCE MONTHLY.
mer of 1871, had confined the larvæ of various species of moths, and neglected to supply them with food for four or five days. These larvæ had advanced toward their final change, possibly within a week or ten days. When the box was opened, the greater number were found in cocoons, while the remainder wandered about, as if in quest of food. The latter the author removed to another box, where they were provided with abundance of food. After three or four days they began to assume the chrysalis form. The first batch proved to be males without exception, while the last batch proved, with but two exceptions, to be females. (The whole number in the two batches was about sixty.)
Mr. Gentry then details further experiments made by him to decide this question, and states that the result was always the same. He adds the following facts, which came under his notice in the course of his observations and experiments: 1. That males are the invariable result when the larvae are fed on diseased or innutritious food; 2. That in the fall, when the leaves have not their usual amount of sap, males are generally produced; 3. That more males are produced late in the season than females; 4. That the sexes, in early life, cannot be distinguished, the change being brought about, late in life, by the conditions of nutrition.
Intensity and Patience required in Scientific Work.—Whether in original work or in elaborating work already done, scientific labor, when conscientiously performed, is necessarily slow and exhausting. M. de Candolle, the great French botanist, has recently brought to a conclusion, with the seventeenth volume, his great "Prodrome of Plants," stopping at the completion simply of the Dicotyledones. It was begun by his illustrious father, Augustin Pyramus de Candolle, about 1816, who worked at it until his decease, in 1841. It was continued by his son Alphonse, who called to his aid other famous botanists, his son Casimir among them. With true naïveté the author pleads necessity of stopping at the point now reached—"ne tertiam botanicorum generationem occideret!"—lest the undertaking should kill off a third generation of botanists. In a supplemental pamphlet he gives his opinion that the Phanerogams, estimated at 110,000 species, might, by distributing the task among twenty-five botanists, be worked up in about fifteen or sixteen years. He says that in his father's time one could elaborate at the rate of ten species a day, but that now a faithful monographer (or specialist), under the modern requirements, can seldom exceed 300 or 400 species per annum—that is, about one species a day!
Rationale of Double Flowers.—That the tendency in plants to produce double flowers is a natural one, and not exclusively evoked by the florist, is shown by Mr. Thomas Meehan, in a communication to the Philadelphia Academy of Natural Sciences. Many of the commonest wild flowers, which no one would think of cultivating, have double flowers in cultivation, which were no doubt originally found wild; for instance, various species of ranunculus. The author had himself placed en record the discovery, wild on the Wissahickon, of a double Saxifraga Virginica, and Dr. James Darrach had found in the same location a double-trailing arbutus. There are in plants two methods by which double flowers are produced. The axis of a flower is simply a branch very much retarded in its development, and generally there are, on this arrested branch, many nodes between the series forming the calyx, or corolla, and the regular stamens and carpels, which nodes are entirely suppressed. But, when a double flower is produced, sometimes these usually suppressed nodes become developed, in which case there is a great increase in the number of petals, without any disturbance in the staminal characters. But, at other times, there is no disturbance of the normal character of the axis. This was the case with the trailing arbutus discovered by Dr. Darrach.
Land-Plants in Lower Silurian.—It has hitherto been supposed that the Silurian age was one in which an absolutely unbroken ocean enveloped the earth. Dr. Dawson made it probable that land-plants existed in the Upper Silurian, or latter Silurian age. Leo Lesquereux, in American