OAK PRUNER. 



OAT. 



about 77 per cent, of tannic acid ; the cellular 

 layer, lying upon the liber, yields only 56 per 

 cent; and the cuticle little or none. Dr. Hig- 

 gins obtained 108 parts of tannic acid from the 

 bark of an oak felled in the spring, and only 

 30 from an oak felled in winter. When the 

 bark is set up to dry, the air, aided by mois- 

 ture, acting upon the tannic acid, converts a 

 portion of it into gallic acid, which is not origi- 

 nally a constituent of oak bark. See BARK 

 and TAN. 



OAK PRUNER. The ground beneath black 

 and \vhite oaks is, says Dr. Harris, often ob- 

 served to be strewn with small branches, neat- 

 ly severed from these trees, as if cut off with 

 a saw. Upon splitting open the cut end of 

 a branch, in the autumn or winter after it 

 has fallen, it will be found to be perforated 

 to the extent of six or eight inches in the 

 course of the pith, and a slender grub, the 

 author of the mischief, will be discovered 

 therein. In the spring this grub is transformed 

 to a pupa, and in June or July it is changed to 

 a beetle, and comes out of the branch. The 

 history of this insect was first made public by 

 Professor Peck, who called it the oak-pruner, 

 or Slenocorus (Blopkidion) putator. See PI. 16, 1. 

 In its adult state it is a slender, long-horned 

 beetle, of a dull brown colour, sprinkled with 

 gray spots, composed of very short close hairs ; 

 the antennae are longer than the body, in the 

 males, and equal to it in length in the other 

 sex, and the third and fourth joints are tipped 

 with a small spine or thorn ; the thorax is 

 barrel-shaped, and not spined at the sides ; and 

 the scutel is yellowish-white. It varies in 

 length from four and a half to six-tenths of an 

 inch. It lays its eggs in July. Each egg is 

 placed close to the axilla or joint of a leaf- 

 stalk or of a small twig, near the extremity of 

 a branch. The grub hatched from it penetrates 

 at that spot to the pith, and then continues its 

 course towards the body of the tree, devouring 

 the pith, and thereby forming a cylindrical bur- 

 row, several inches in length, in the centre of 

 the branch. Having reached its full size, 

 which it does towards the end of the summer, 

 it divides the branch at the lower end of its 

 burrow, by gnawing away the wood transverse- 

 ly from within, leaving only the ring of bark 

 untouched. It then retires backwards, stops 

 up the end of its hole, near the transverse sec- 

 tion, with fibres of the wood, and awaits the 

 fall of the branch, which is usually broken off 

 and precipitated to the ground by the autumnal 

 winds. The leaves of the oak are rarely shed 

 before the branch falls, and thus serve to break 

 the shock. Branches of five or six feet in length 

 and an inch in diameter, are thus severed by 

 these insects, a kind of pruning that must be 

 injurious to the trees, and should be guarded 

 against, if possible. By collecting the fallen 

 branches in the autumn, and burning them 

 before the spring, 'we prevent the develope- 

 ment of the beetles, while we derive some 

 benefit from the branches as fuel. 



Oak trees are also subjected to the attacks 

 of insects, which destroy the leaves, deposit 

 their eggs in the branches which they destroy, 

 and others which devour the solid wood. See 

 BEKTLKS, BORERS, CATERPILLARS, LOCUSTS, &c. 

 854 



I OAT (Russ. mves ; Pol. owies; Dutch, Jiaver i 

 ! Fr. Avoine Lat. avena). A very valuable cereal 

 grass, of which several varieties are cultivated 

 for their seeds: the chief of these are 1. The 

 Avena saliva, or common oat. PI. 3, e. 2. The 

 A. orient alls, or Tartarian oat, /. 3. A. strigo'Oj 

 or bristle-pointed oat. 4. A. brevis, or short oat, 

 5. A- nuda, or naked oat. 



The common oat is far the most important 

 of these species. Its spikelets contain two or 

 three seeds. Its florets are sometimes furnished 

 with awns, and at other times are awnless. The 

 oat is a native of cold climates : it flourishes 

 in the temperate latitudes, but it degenerates, 

 and at last refuses to yields profitable crops as 

 it approaches the equator. It is, however, cul- 

 tivated with success in Bengal, as low as the 

 25 of latitude. It flourishes remarkably well 

 in Ireland and in Scotland, and constitutes the 

 principal food of the inhabitants. In England 

 it is cultivated to a very considerable extent in 

 the fen districts of the eastern counties, as well 

 as in the northern border districts, in which 

 last the oats are considered to be very superior. 

 By cultivation, difference of soil and climate, 

 and other causes, the common oat (A. saliva} 

 has produced several varieties, which have 

 been divided by some authors into three classes, 

 the black, the gray, and the white. Those of 

 the first class are commonly hardy, have small 

 seeds, become early ripe, and are hence well 

 adapted for cold hungry soils, such as those 

 which are usually found on considerable ele- 

 vations. 



The gray, or dun-coloured oats, although 

 possessing more valuable qualities than the 

 black oat, are still inferior in quality to the 

 white, but on some soils yield very remunera- 

 tive crops. 



The third and most valuable class of oats is 

 the white. " The most improved of these," says 

 Professor Low, " are without awns. They are 

 the least hardy kinds, but they are of the 

 greatest weight to the bushel, and the most 

 productive of meal. In this class the potato 

 oat is that which has possessed the greatest 

 reputation for a time in the districts where it is 

 cultivated. It is not so well suited to inferior 

 soils as some of the other white and darker- 

 coloured kinds: it is also less productive of 

 straw, though the grain is more plump, weighs 

 heavier, and yields a greater weight of meal. 

 The hardier kinds, however, are better suited 

 to certain situations than the finer, just as the 

 hardier red wheats are better suited to certain 

 situations than the thin-chaffed and white varie- 

 ties. The potato oat was the discovery of ac- 

 cident, and the produce of a single plant. It 

 has, in many cases, shown a tendency to de- 

 generate, by the husks becoming thicker and 

 the body less plump, and by the partial appear- 

 ance of awns." 



The Poland oat is another valuable cultivated 

 variety of the white oat. It comes early to 

 maturity, and is a prolific bearer. Its defects 

 are a tendency to be deficient in straw, and a 

 liability to shed its seeds. 



Besides these there are several other varie- 

 ties of the white oat, as the Dutch, or Friesland 

 oat, the Hopetoun oat of East Lothian, &c. 



The Hopetoun oat was produced in 1824, by 



