PLANING MACHINE entirely free from disease. There are several varieties, one of which, var. acerifolia, so close- ly resembles P. occidentalis as to be sold for it in England. The wood of the oriental plane, being hard, close-grained, and capable of a fine polish, is much valued for furniture and join- ery, and in the East is used in ship building. The remaining species are P. Lindeni, very near P. occidentalis, and P. Mexicana, which has two balls upon a peduncle 5 or 6 in. long, both natives of Mexico. The planes may be multiplied by cuttings and by layers, but they are usually propagated from the seed. PLANING MACHINE, a machine for planing lumber by mechanical power. One of the earliest forms, invented by Gen. Bentham of England in 1791, drove a slightly modified hand plane. A machine patented by Mr. Bramah in 1802 performed its operation by the rotation of a vertical spindle, carrying at its lower extremity a horizontal wheel, the rim of which was furnished with 28 cutters or gouges, which were followed by a plane also attached to the wheel. Thus the rough surface of the board was trimmed and left perfectly smooth as it was carried by suitable mechanism from end to end. American patents were oc- casionally granted for planing machines from the year 1800 to 1828, when William Wood- worth of New York patented the celebrated Woodworth planing machine. This performs its operation by the use of cylindrical cutters, or cutters attached to a horizontal shaft re- volving with great velocity while the board is borne along under and in contect with them by means of two or more horizontal rollers, which clamp the board on either side, the roll- ers being driven by mechanism communicating motion from the cylinder. Though the cylin- drical machine was not originally invented by Woodworth, his claims covered such essential improvements in some of its details as to ren- der the patented modifications invaluable, and thus gave him an almost exclusive monopoly. In 1829 Uri Emmons obtained two patents, one for cylindrical and one for circular pla- ning machines. In 1836 Thomas E. Daniels of Worcester, Mass., greatly improved the Bra- mah or circular machine. The Daniels planer is usually constructed with but two cutters, and the plane of the Bramah machine is entirely dispensed with. It is still preferred for cabi- net and other fine work. Many attempts were made to supersede the Woodworth machine by the use of stationary cutters, but for ordinary practical purposes the former are preferred. The patent right of the Woodworth machine was sustained by the courts during a term of 18 years, under the original patent of 14 years and two renewals of 7 years each. Numerous improvements are annually added to these ma- chines, descriptions of which may be found in the patent office reports. PLANT (Lat.planta), an organized being origi- nating from a germ and nourished solely by in- organic substances. Although the differences 667 VOL. xiii. 37 PLANT 573 between plants and animals in their higher forms are sufficiently obvious, with the lower ones it is difficult in many cases to decide whether an object ought to be classed as a plant or as an animal. Motion, which was formerly regarded as belonging only to ani- mals, is now known to be a characteristic of some vegetable forms, and chemical constitu- ents at one time supposed to belong only to plants have been found also in animals. Thus far it is not known that any animal can subsist directly upon the elements furnished by the mineral kingdom, while the plant is able to live upon air, water, and other inorganic materials, and assimilate them, converting them into or- ganized structure, which may serve as food for animals ; in doing this the plant takes in and decomposes carbonic acid, fixes carbon, and gives off oxygen, a function not known to be- long to animals. Most animals have a stomach or internal cavity into which organized food is received ; plants have no special receptacle for their food corresponding to a stomach. Development of the Lower Plants. The plant in its most rudimentary form consists of a semi-fluid substance, protoplasm, surrounded by a cell wall a mi- nute sac or bag of protoplasm; in chem- ical constitution the cell wall is a carbo- hydrate, known as cellulose, its compo- sition being carbon, oxygen, and hydro- gen; the contents of the cell belong to the proteine compounds, and, besides the ele- ments of cellulose, contain nitrogen. An illustration of these simple forms of plant life is found in proto- coccus, which when present in large numbers appears as a green or even red scum, or in torula, the yeast plant. These plants, though so simple in structure and so insignificant in size, some of them not over -nj-.^nr of an inch in diameter, while others are as large as -^Vg- of an inch, perform the two principal func- tions of larger and more complex plants : they grow and reproduce themselves. Being sur- rounded by a liquid (in the case of protococcus by rain water, which contains carbonic acid, ammonia, and other matters in solution), the little plant absorbs its nourishment through the cell wall; it increases in size by assimilating its food ; small as it is, it can decompose car- bonic acid, appropriating the carbon and set- ting free the oxygen, and combining this with the other elements form cellulose and proto- plasm, which incorporated with that already in the plant increases its bulk to the full size proper to the species. When growth is at- tained, reproduction commences; the proto- plasm subdivides into two, four, eight, or more masses, around each of which a cell wall is- FIG. 1. Protococcus. 'lant of a single cell, mul- tiplying by subdivisions (magnified.)
