Page:Popular Science Monthly Volume 6.djvu/654

636 those who started with half-developed powers and half-furnished minds.

Insects and Flowers.—In his lecture at Belfast, on "Common Flowers in Relation to Insects," Sir John Lubbock inquired into the causes of flowers closing their petals during rain, and of some flowers remaining open for a longer or shorter period than others. The habit of closing the petals during rain is obviously an advantage, since it prevents the honey being spoilt or washed away. Everybody, however, has observed that even in fine weather certain flowers close at particular hours. This habit of going to sleep is surely very curious: why should flowers do so; and why should some flowers close at the approach of night, and others not? Moreover, flowers keep different hours. The daisy opens at sunrise and closes at sunset, whence its name day's eye; the dandelion opens at seven and closes at live; ear hawkweed is said to wake at eight and go to sleep at two; the scarlet pimpernel wakes at seven and closes soon after two; while Tropogon pratensis opens at four in the morning and closes just before twelve, whence its English name "John-go-to-bed-at-noon." Other flowers, on the contrary, open in the evening. Now, it is obvious that flowers which are fertilized by night-flying insects would derive no advantage from being open by day; nay, it would be a distinct disadvantage, as rendering them liable to be robbed of their honey and pollen by insects not capable of fertilizing them. Hence the lecturer believed that the closing of flowers has reference to the habits of insects. In support of this, he observed that wind-fertilized flowers never sleep, and that some of those flowers which attract insects by smell emit their scent at particular hours.

Catching Cold.—We find, in the Detroit Review of Medicine, an account of Prof. Rosenthal's researches on the effects of sudden changes of temperature, from which we abstract a few very useful observations. It has long been known that "colds" are produced, not by lowness of temperature, but rather by sudden changes from a higher to a lower. The application of cold to the surface of a healthy animal causes the cutaneous vessels to contract, and then the blood is prevented from circulating in the skin, and confined to the interior of the body, where it does not readily lose its heat, but serves to supply warmth to the vital organs. But, if the animal be exposed to heat, the cutaneous vessels become dilated, and so remain after exposure to cold. The blood is thus exposed in large amount over a wide surface, and becomes rapidly cooled, even though the temperature of the surrounding medium is not very low. A sudden passing from a heated room into the cold outer air rapidly cools the blood below the normal degree. As it returns to the internal organs, it cools them much more quickly than it would have done were not the vessels dilated by previous warmth. Thus a sudden cooling of the blood produces an irritating effect, or induces inflammation in a way that a gradual alteration would not do. To produce evil results the cooling must be from above to below the normal temperature. The effect of a chill in causing inflammation may be due partly to the effect of cold on the tissues themselves, and partly to the congestion (hyperæmia) which will occur in some parts when the fluid is driven out of others by the contraction of vessels. Rosenthal lays most stress on the former of these effects. It is a well-known fact that frequent cold bathing or sponging enables one to bear with impunity sudden changes of weather. This is explained by the improved tone of the vessels, produced by the cold applications. Thus, when exposed to heat, they are not so relaxed that they cannot sufficiently contract when necessary.

Blow Plants are distributed.—Some low ground on the banks of the Delaware, below the city of Philadelphia, having had a quantity of mud from the channel of the river spread over it, two species of plants, Polygonum Orientale (an East Indian species), and Cleome pungens (a West Indian species), soon made their appearance in great numbers. During a discussion, in the Philadelphia Academy of Sciences, as to the probable origin of the seeds of these plants, Dr. Leidy expressed the opinion that as the ground had long been used as a place of deposit of ships' ballast, the seeds might