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BIRCH again answered in the negative, as it had been in the 18th century, and finally it was put to rest through the work of Pasteur, Tyndall and others.

In the latter part of the century experiments on living forms became prominent. The eggs, the larvae and the older stages have been placed under different conditions of temperature, light, food, chemical and mechanical surroundings, and the effect of these changes watched. Many important facts have been brought to light by these experiments.

Biology is a body of rapidly expanding knowledge of intense interest and great service to mankind. Much was accomplished by it in the 19th century, but much more is to be expected in the 20th century.

For books about biology, see Sedgwick and Wilson's General Biology, Parker's Elementary Biology and Thompson's The Science of Life. Additional titles will be found under, ,.

 Birch, species of the genus Betula, which consists of trees or shrubs, very widely distributed throughout the north temperate regions. The birches have usually a bark which separates in thin papery plates, and the long and pendulous catkins of flowers appearing in very early spring are well known. They grow in North America, Europe, North and Central Asia. Bailey states that no tree grows farther north than the birch. The Dwarf Birch is highly valued by the Laplander, furnishing him most of his fuel, and its tiny nut furnishing food for that bird so useful to the Laplander, the ptarmigan. The wood of many birches is inferior owing to the toughness of the bark interfering with the evaporation of the sap, its consequent fermentation and the crumbling of the wood. It makes excellent fuel; is used in manufacture, and is employed for furniture and small, common articles. Of the bark are made baskets, boxes; and that of the Paper Birch is extensively used for canoes; a dye is also made of it, and an oil which is used in the preparation of Russia leather. A number of birches are cultivated as ornamental trees, the weeping birch being extensively planted in this country. They are graceful of form, fair appearing from bark to least tremulous leaf. They are easily propagated by seeds and grow rapidly.

The American White Birch has a short life, but is a graceful tree and plucky one, springing up in deforested land and abandoned fields. It grows south as far as Pennsylvania. It is a small tree, from 25 to 45 feet high, the bark smooth and white, not readily peeling; foliage tremulous; dark green, triangular leaves, turning yellow in autumn. Recently the wood has come into value, found useful as wood pulp, for shoe-pegs and spools.

The Canoe Birch or Paper Birch is one of the largest and most picturesque of the birches, and is widely distributed throughout our northern states. It usually grows to a height of from 60 to 80 feet, sometimes reaches to 120 feet; its bark a conspicuous chalky white, which tears off readily in horizontal sheets. The leaves are large and broadly ovate. This, as the name suggests, is the tree so friendly to the Indians, giving them bark for their famous canoes, for their shelters, and for their household utensils, giving them fuel that quickly crackled and flamed; even giving them food, they making this use of the layer between wood and bark (cambium). The Indians to-day still make canoes of birch bark, baskets and various other articles thereof. The bark, as is well known, tears off in thin sheets of several layers, the thinner ones being frequently used as letter paper, a use of birch bark going back to ancient times. The peeling of the bark by careless hands, cutting too deep, results in the loss of many goodly trees, whose far-gleaming white columns have proved their undoing.

The Cherry Birch is a comely tree and useful as well as ornamental. It is sometimes known as Sweet Birch, also as Black Birch. It grows from 50 to 80 feet high, and is noted for its grace and symmetry. The bark of this birch is dark brown, the leaves, from two to five inches long, are oblong-ovate. Early in the spring the Black Birch is all aglow with yellow catkins, it is all golden in the fall, in the summer it bears an abundance of glossy foliage. In the spring the children find the winter-green flavor of the saplings very pleasant to the taste. The sap is made into birch beer, and from the inner bark are obtained salicylic acid and wintergreen oil. The hard, strong wood, of good red-brown color and taking a fine polish, is sometimes used for furniture, and is employed for wheel hubs and fuel. The range of the tree is from Newfoundland to Ontario, south to Florida, Kentucky, Tennessee and Kansas.

Other varieties are the Yellow or Gray Birch and the Red or River Birch. See Bailey: Cyclopædia of American Horticulture and The Tree Book by Julia E. Rogers.  Bird Day, a day set apart for the purpose of interesting boys and girls in wild birds and in bird protection. The idea of Bird Day originated with Professor C. A. Babcock of Oil City, Pa., who in 1894