BARKER'S MILL 



592 



BARLEY 



the strain of the enlargement due to inner 

 growth, then stretches and tears. That strain, 

 together with the action of sunshine and rain, 

 causes the rough, tattered appearance of old 

 tree trunks. 



When a tree is chopped down and cut 

 straight across, a number of quite distinct rings 

 will be seen in the wood, one within the other. 

 These rings show the fresh yearly growths of 

 the inner bark and by counting them the age 

 of the tree can be ascertained. 



Marly man used barks for most of the neces- 



> of life. Some were made into clothing 



others furnished lire. Some were 



made into weapons or canoes; others furnished 



valuable medicines. Many of these uses have 



been repeated from generation to generation 



until the present time. 



Some barks are valuable in commerce. Cork 

 is gathered from the outer layer of the bark of 

 certain oak trees. Tannic acid, the substance 

 which is valuable in tanning leather, is obtained 

 from the bark of hemlock and other trees. 

 Quinine is made from Peruvian bark; cough 

 mixtures from cherry bark. Bark is the source 

 of the cinnamon of commerce, a popular flavor- 

 ing ; and the bark fibers of hemp, flax and other 

 plants are made into threads, ropes, mats and 

 cloths. 



Injurious Insects. The rough bark of trees 

 furnishes a home for insects, many of which are 

 injurious to plant life. The insect enemies of 

 the apple, alone, are estimated at over 300. 

 These destructive insects are well represented 

 by the San Jose scale, which attacks the inner 

 bark. Elm trees are especially subject to 

 attacks of injurious insect pests. In many 

 localities folded burlap bands of cloth are put 

 around parts of the trunks of these trees. Insect 

 grubs crawl into the bands and can in that 

 way be removed and destroyed in large num- 

 bers. Another serious pest is the bark beetle, 

 which burrows between the bark and wood or 

 makes a tunnel through the wood. In these 

 crevices the female deposits her eggs. Both 

 ire and young insects are very destructive. 

 See INSECTS; SAN JOSE SCALE; APPLE, subhead 

 Destructive Insects. M.S. 



BARKER'S MILL, a mechanical device in- 

 vented near the end of the 'seventeenth cen- 

 tury by a Dr. Barker, to illustrate the prin- 

 ciple of reaction (see DYNAMICS). It consists 

 of a vertical tube supported by an arm which 

 attaches it to a vertical support. On the lower 

 end of the vertical tube is a hollow block, from 

 which short, curved arms extend. The outer 



openings of these arms all face in the same 

 general direction. The contrivance is mounted 

 on a frame so 

 that it can rotate 

 about the vertical 

 axis. When 

 water rushes into 

 the vertical tube 

 from the reser- 

 voir, the reaction 

 caused by the 

 discharge of the 

 water jet from 

 the orifices in the 

 arms causes each 

 arm to move 

 backward and 

 thus makes the 

 apparatus 

 revolve. This de- 

 vice is used ex- 

 tensively in auto- 

 matic lawn 

 sprinklers, auto- 

 matic sprinkler 

 systems for busi- 

 ness buildings, 

 and other forms 

 of apparatus for 

 throwing water. 



BARLEY, a grain fifth in importance 

 among the world's cereals, being greatly ex- 

 ceeded by oats, wheat and corn, and slightly 

 by rye. Barley does not differ greatly from 

 wheat. It was known among all ancient peo- 

 ples; in Deuteronomy we read that the Prom- 

 ised Land was a "land of wheat and barley." 

 The sacred books of China mention that it was 

 cultivated in that country twenty centuries 

 before the beginning of the Christian Era. 



Barley is grown over a wider area than any 

 other grain, for profitable cultivation is possible 

 from the equator to 70 north latitude. A 

 very high quality is grown in Canada, where 

 the crop averages 45,000,000 bushels yearly. 

 In the United States about 200,000,000 bushels 

 are raised in a year; North Dakota, Minnesota, 

 California, South Dakota, Wisconsin and Iowa 

 lead in its production. In the United States it 

 ranks fourth among the grains, and in Canada 

 is third in importance. 



Cultivation. In the United States, Canada 

 and most parts of Europe barley is usually 

 sown in spring, after danger of severe frosts is 

 over. But this grain is more suited to cold 

 latitudes than any other. The coarser varieties, 



BARKER'S MILL 



