Page:Popular Science Monthly Volume 49.djvu/739

Rh. M. Gain further found that moisture in the soil favors and increases the number of fruits and seeds, while a dry soil promotes larger and heavier seeds. Plants in dry soil have more roots than those in wet soil. While the tenure of moisture has little influence on the number of tubers, they are larger and heavier in a moist soil; yet they are less perfect than tubers grown under relatively dry conditions. Thus, while greater moisture is favorable to a larger immediate return, it is less promotive of perfection in the reproductive parts, and so favors the individual rather than the vigor of the species.

Geography in the Middle Ages.—The first number of Herr M. Konrad Miller's work on the Oldest Maps of the World is devoted to the map of the universe of St. Beatus, a Spanish theologian, who died 798. It was made in connection with the author's Commentary on the Apocalypse, to point out the regions assigned to the several apostles, and exists in many copies of different ages, the maps in which differ but little from one another. One of the most famous of these copies is the one called the Manuscript of St. Sever, in the Bibliothèque Nationale, Paris, of about 1050. The map includes the whole world in an oval inclosed by a blue sea border containing large and fierce-looking fishes and red objects which might be taken for red slugs, but which are really vessels. At the extreme east (north and south being at the ends of the axis of the oval) Temptation is represented in a naturalistic style. At the point where the earthly paradise was supposed to exist, Adam is bashfully making symbolical gestures, and Eve, bold and full of initiative, is picking the apple, both entirely naked. It appears clear as the light of the sun that all the wrong is on Eve's side. In the extreme west are Tangier and Cordova at the entrance of a sea that washes Majorca and Minorca, then Sardinia, Corsica, Cyprus, and Crete, and turns to the north in the Adriatic Gulf and the Hellespont. The Fortunate Islands, in the midst of numerous fishes, are Madeira and the Canaries, and, together with the British Isles and perhaps Iceland, mark the western limit of the world. In the south the Red Sea, bright scarlet, is separated from the Mediterranean by the whole of Egypt and Palestine in a way to defy the most enterprising isthmus-borers. No pains are taken to give the contours of the coasts, the bays, or the gulfs. Spain is reduced to a triangle, one side of which, curved, is formed by the Pyrenees, as if they were a fringe, while the other two sides are the shore, straight. The details of the geography of the several countries are curious, but can not be described here. Many strange things appear in Africa, too, while the origin of the Nile in a great lake is indicated in the clearest manner.

Origin of Honeydew.—M. Gaston Bonnier's studies of the formation of honeydew have led him to the conclusion that not only is it elaborated through the agency of aphides, but it is also exuded directly, under proper conditions, by the leaves of the trees. He has observed that under conditions of a considerable difference between the temperatures of the day and the night, when no insects can be found, a sugary liquid falls after sunset in drops from certain trees; and after wiping the leaf with absorbent paper, he found the minute droplets issuing from the stomata. This was observed on the epiceas, silver firs, Scotch pines, Austrian pines, oaks, maples, aspens, poplars, alders, birches, vines, and various herbaceous plants. Yet the aphides are the more frequent-cause of the production of honeydew. Their work is done mostly in the daytime and is suspended during the night, while the direct production of honeydew takes place at night and ceases in the daytime. It is promoted by the interposition of cool nights between hot and dry days, and is favored by increase in hygrometric conditions and darkness. The exudation can be provoked artificially by dipping the branches into water and then placing them in the dark in a saturated atmosphere. Under these conditions the leaves may be caused to produce honeydew when those on the trees from which they were taken do not. Although bees will go to collect any sweet substance when they can get no better, they always prefer the best they can find. When mellifluous plants are blooming abundantly, they pass the honeydew by; but when mellifluous flowers are scarce, they gather honeydew. The chemical composition of honeydew is various; but that naturally exuded approaches that of the honey