VOL.4, No. 6
RELATION OF CHEMISTRY TO AGRICULTURE
729
R a n k i n g a m o n g the elements of highest importance to the crop stands carbon. Upon carbon, available to vegetation as carbon dioxide, the p l a n t is dependent for its sugar manufacture. The normal concentration of carbon dioxide in the atmosphere varies, according to Lundegardh, from 0.0256 to 0.0329 volume p e r cent. If this concentration is increased, gratifying results almost invariably follow, the plants reaching m a t u r i t y i n an amazingly s h o r t time. About 1918, Riedel, in Essen, obtained flue gases from a steel factory, purified them, a n d piped t h e m into an adjoining field of beets, with surprising increase of yield. Perhaps more than any other phase of argicultural chemistry does the principle demonstrated by Riedel demand development, f o r by its successful application t h e crop yield of the world may b e greatly augmented, and at once the smoke nuisance of our cities-an ever-increasing m e n a c e b e diminished.
Fast-Growing Trees Bred for Paper and Rayon Uses. Fast-growing hybrid poplar trees grown as a farm crop may before long compete with corn and cotton for a place in the fanner's fields. Dr. A. B. Stout of the New York Botanical Garden. Dr. Ralph H. McKee of Columbia University, and E. J. Schreiner of the Oxford Paper Company, announce that they have succeeded in obtaining new hybrid varieties of poplar that will reach a trunk diameter of eighteen inches in eighteen years, giving a total yield of 100 cords to the acre. Part of the crop can be harvested a t the end of ten years, to thin out the stand, and the balance when the trees have matured. The unusually rapid growth of the new varieties, the investigators explain, is due to a phenomenon, long known to breeders, called "hybrid vigor." It is not a t all well understood, hut in plant and animal husbandry it is much used to obtain thriftier crops and stronger and larger livestock than can he got by sticking to unmixed species. The superior strength and endurance of the mule, a hyhrid between the horse and the donkey, are credited to this hyhrid vigor, and many of our best field and garden crops have heen obtained in the same way. A few tentative experiments have been made in the past with hyhrid forest trees, hut the present work is the first endeavor to apply the principle to the development of a tree needed for a group of major industrial operations.-Science Seruice Measures Ten-Millionth of Degree of Temperature. Using an electrical heatmeasuring device so incredibly delicate that it is sensitive to two trillionths of an ampere of current and will measure temperature changes of as little as one ten-millionth of a degree Centigrade, Dr. A. V. Hill of the Cornell University has measured the temperature changes in nerve fibers during their activity. In describing his experiments before the National Academy of Sciences, he stated that his object had been t o learn more about the nature of nervous action. Older theories have held that nervous impulses were not like other physiological processes, but were physical waves like light or radio waves. These ideas were based on the absence of any detectible heat given off by nerves as a result of stimulation. But with the extremely sensitive instrument devised by Dr. Hill it is possible to measure the almost vanishingly minute temperature rise that occurs in a single nerve fiber when it is caused to react The moment of activity of a nerve is followed by a prolonged period of recovery, during which nine times the initial amount of heat is given off.-Science Senice
