have to-day supplanted pitch and tar, the chief products of this industy in colonial times in the United States.1 But the descriptive name, naval stores, given when these commodities were used extensively in the construction and maintenance of sailing vessels, still persists. That mankind has long made use of these forest products appears from the descriptions of the production and uses of pitch contained in ancient writings.2 As long ago as the fifth century before Christ, the pines of Macedon were a famous source of pitch. During the period 315 to 166 B. C., Macedon is recorded to have had a distinct monopoly of wood and pitch, which highly valued and important commodities could not be exported without special permission from the ruler. Pitch was obtained by destructive distillation of the heartwood or of especially pitchy chips from wounded trees, or by driving off the water from the exuded gum. Pitch was in great demand for calking the seams of ships, including the war ships of the period, as is related in the case of the "wooden walls of Athens at Salamis." It was also used, for example, as a surface coating for altars and doors or as a sizing or lining for clay storage jars, used as containers for grain and other supplies.

3

Until rather recently many of the methods used in the early days of the industry in this country were still in vogue. The cup method, introduced on a commercial scale about 1904, has, however, of late largely supplanted the wasteful box system. (See Pl. I, fig. 1.) Another much-needed improvement is seen in the tendency to reduce the amount of wood removed when the trees are scarified or chipped. The success of this practice has been demonstrated by experiments and the experience of progressive operators. In order to determine the best methods of turpentining, a comprehensive understanding of the tree's responses must be obtained. This involves thorough research of problems bearing on many aspects.

PURPOSE OF THE INVESTIGATION.

The investigation here described is concerned primarily with the comparison of the results of experiments with three different methods of chipping. It is shown that the success of a method can not be judged merely on the basis of the yield obtained. The maintenance of wood production, as indicated by growth in height and in diam

1 Public Record Office, London, 1610. "Instructions for suche things as are to be sente from Virginia." Also " Booke of the Commodities of Virginia' (cited from U. S. Dept. Agr. Bul. 229.)

2 Theophrastus: "Enquiry into Plants" III, IX, 1-3 and IX, II & III. Plini: Naturalis Historia XVI.

3 Glotz, G.: "L'Histoire de Délos d'après les Prix d'une Denrée." Revue des Études Grecques. Tome XXIX. Juillet-Septembre, 1916. (Reviewed by Gerry, E. Jour. For. 19:

April, 1921, p. 438.)

Herty, C. H.: "The Turpentine Industry of the Southern States." Jour. Franklin Institute. March, 1916.

eter, and the preservation of the general health of the tree are considerations of fundamental importance. This is especially true with reference to the methods that are to be used in the future for turpentining smaller, second-growth trees. The need for wider knowledge and the practice of better methods is imperative in the United States, in order that this important and exceptional opportunity for the production of naval stores shall not be wiped out or wasted by improper exploitation.5

The work covered was undertaken in order to obtain, by means of microscopic study, information on the changes which result from turpentining in the wood of the pines, which are the chief sources of naval stores. The advantages and disadvantages of different methods of operation were determined chiefly by examining specimens of the wood produced near the faces or scars. These specimens were usually cut just above the streak or surface of the last wound. Structures found on workings of different ages were also studied. The specimens furnished evidence which served as a check of considerable precision upon the more general means of comparison, such as amount of gum produced and percentages of dead and dryfaced trees caused by turpentining. Changes produced by turpentining which were registered in the internal anatomy of the pines were studied, not only in the completed annual ring at the end of the season, but also particularly in specimens obtained periodically throughout the year. The first material was cut before wood formation began in the spring, and the development shown in fresh specimens cut each month thereafter was studied throughout the subsequent growing season. The chief source of material was a cooperative experiment carried on at Columbia, Miss., where three methods of chipping were compared, but specimens were also collected at other points in Mississippi and in Louisiana and Florida.

An attempt was also made to determine the significance of certain observations made at the Forest Products Laboratory not in accord with views previously published, some of which were founded upon analogy rather than upon the study of native American species."

OLEORESIN.

The exudation obtained by the systematic scarification of the living pines, especially longleaf pine in the United States, is variously known as "oleoresin," "gum," "dip," and " ," "dip," and "scrape" (when hardened after long exposure to the air). From this substance rosin

5 Approximately 75 per cent of the world's supply of gum turpentine is made in the United States. i

See pp. 12 to 25.

7 Herty, C. H., "Relation of Light Chipping to the Commercial yield of Naval Stores," For. Ser. Bul. 90, 1911. Tschirch, A., “Die Harze u. d. Harzbehälter," 1900.

and turpentine are obtained as the products of distillation. The "gum turpentine" distilled from oleoresin is distinguished from "wood turpentine," which is obtained from the steam or destructive distillation of the resinous heartwood of stumps or dead or down timber.

Fresh gum spirits of turpentine distilled from the southern pines of the United States consists of several similar or closely related compounds known as terpenes, together with small and varying quantities of oxidized derivatives thereof. The empirical formula of the terpenes is C10H16, indicating that turpentine consists almost entirely of carbon and hydrogen. Of the terpenes, the one known as pinene occurs in the highest proportion in spirits of turpentine. Alpha pinene is found to the extent of 80 to 85 per cent in the average pure, fresh, American gum spirits of turpentine. Among the other terpenes which have been found in small quantities in turpentine oil may be mentioned beta pinene, camphene, silvestrene, and dipentene, the last two being found also in destructively distilled wood turpentine. American pinene, the greater part of which is obtained from longleaf pine (Pinus palustris) gum, has optical properties different from those of the French. The pinene from slash pine (Pinus caribaea), however, resembles the French in this particular. Otherwise the turpentine oils of slash and longleaf pines are very similar, whether obtained from the wood or from the leaves."

STRUCTURE OF WOOD OF TURPENTINE PINES.

Of fundamental significance for the understanding of the production of naval stores is the structure of the wood of the pine, especially of Pinus palustris Mill. (longleaf pine), and Pinus caribaea Morelet (slash pine), which are the chief turpentine pines of the southern United States and produce approximately 75 per cent of the world's supply of naval stores.10 It is from the outer wood next the bark in the living pine that oleoresin is obtained. Here also the responses to turpentining, differing according to the methods practiced, are clearly registered in the woody tissue that is formed after the scarifications have been made.

8 Veitch, F. P., and V. E. Grotlisch, "Turpentine," U. S. Dept. Agr. Bul. 898, 1920. Schorger, A. W., "Constribution to the Chemistry of American Conifers." Trans. Wis. Acad. of Sci. Arts and Letters, 19: March, 1919, p. 742.

10 Oleoresin is also obtained in relatively small quantities from various other species of pine, including: In the United States, P. echinata, shortleaf; P. taeda, loblolly; P. ponderosa, western yellow; and P. serotina, pond pine; in France, P. pinaster or maritima, maritime pine; in Greece and Algeria, P. halepensis, Aleppo pine; in Italy, P. pinea, stone pine; in Austria, P. laricio, austriaca, or nigra, black pine; in India, P. longifolia, chir pine; and P. excelsa, the Himalayan or Bhotan pine; in Mexico and Central America, P. ayacahuite, the Mexican white pine; in central Germany, Poland, and northern Russia, P. silvestris, Scotch pine; and in Japan, P. thunbergii, Japanese black pine. (From U. S. Dept. Agr. Bul. 898.)

PLATE I

FIG. 1.-The old method of cutting a box or cavity in the butt of the tree. Disadvantages: The tree was weakened; it became a fire hazard; the box was difficult to empty; and wasteful as a receptacle for receiving gum from a high face.

FIG. 2.-Stand which includes the trees selected from the narrow, double, and standard chipped tracts at Columbia, Miss., for detailed microscopic study throughout the respective seasons of 1916 and 1917. Note the presence of some suppressed trees.

FIG. 3.-The American practice of placing an "advance streak" some weeks before regular chipping begins. (This picture was obtained through the courtesy of Mr. F. Canning of the Forest Service of India.)

FIG. 4.-Appearance of a tree at the end of a standard 2-year commercial operation, at Columbia, Miss. FIG. 5.-Small or modified American face used experimentally on small timber on the Florida National Forest after 3 years' turpentining.

FIG. 6.-French method of turpentining as practiced experimentally on small timber on the Florida National Forest after 3 years' turpentining. Note shape of face, chipping tool, and area freshened.