150 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



under what conditions exactly these ducts and vesicles arise, and how and why the resin forms, 

 are matters still imperfectly understood. Resin passages begin to develop in the young seedling, 

 and even during germination; resin forms in the growing bud, however, only during normal 

 respiration and growth. It is, then, a product of the living plant, formed by and during its life 

 functions in the living parts of the plant; yet, as far as we know, it is a product of decomposition, 

 which, while perhaps not useless in the economy of the plant, seems to find 710 further use in the 

 nutrition or growth of its organs. 



Resin passages arise from the shrinking away from each other of the walls of neighboring- 

 rows of cells; an intercellular space is thus formed and gradually filled up with products of 

 decomposition and secretion, which we call resin. The source of these secretions is also still more 

 or less unexplained. In the first place it comes, no doubt, from a decomposition of the cellulose 

 of the surrounding cell wall; then the starchy contents of the cells themselves may change into 

 resin, and by oxidation of terpenes, essential oils, the surrounding cells with their contents are 

 liquefied and resorbed, and in this way the resin duct becomes filled and enlarged from a mere 

 intercellular passage to an irregular smaller or larger pocket or canal. The number, size, and 

 arrangement of the resin ducts and vesicles differ with different species. 



The Cupressus genus all have isolated cells containing resin; some have also ducts, the 

 contents of which give the wood its peculiar odor, but these do not contain sufficient quantities 

 to permit extraction except by distillation of the wood itself. One of the Thuya tribe (Callitris 

 quadrivalviii), of Algiers, furnishes the white resin, known as sandarac; and the fruit of the 

 juniper, rich in essential oil, is used iu the preparation of gin, the flavor of which is due to the oil. 



The wood of the firs (Abies) does not contain any resin ducts, only isolated resin cells and 

 vesicles, which are found most amply in the bark, containing an oleoresin very rich in volatile oil, 

 and hence very liquid. The wood of the spruces (Picea) contains few, rather narrow, longitudinal 

 ducts, and wider lateral ducts strongly developed. The larch (Lari.r) contains resin ducts of very 

 large diameter. The largest development of resin passages, however, occurs in the pines (Pinus), 

 admitting extraction on a large commercial scale. 



In these we find longitudinal resin ducts in greater or less abundance, according to the 

 species, iu all parts of the annual rings, more frequently, however, in the summer wood than in 

 the spring wood; hence, in part, the darker coloration of the former. Those of the ducts which pass 

 near a medullary ray form lateral extensions along the cells of the rays, by means of which the 

 longitudinal duets are more or less frequently connected. These lateral ducts extend into the 

 bark, where sometimes considerable pockets of resin are formed; the longitudinal ducts are, 

 however, the most important source of resin supply in the pine. 



As we have seen, the production of resin takes place under the life functions of the tree in 

 the living parts. Whether, and if so how, the resin wanders in the tree is not well known. Small 

 amounts, no doubt, remain at the place where they were formed. Larger masses may change their 

 place, following the law of gravity, although the observation that leaning trees are richest in resin 

 on the under side does not necessarily predicate a wandering. The collection of resin in the 

 hollows of trees (frost pits) of the larch may not be due to a wandering of the resin, but an 

 emptying of broken ducts into the open spaces, in which the counterpressures otherwise existing 

 ;irc relieved. 



The special investigations undertaken in the Division of Forestry, and recorded in Bulletin 8, 

 and reproduced in a later part of this report, have shown that the quantitative distribution of 

 resin throughout the tree, from top to bottom, follows no law, the larger amounts being as often 

 found in the top or middle portions as in the butt-logs. 



If the claim that the roots and base parts are richest in resin be a fact, this need not be 

 due to a wandering of the resin, but to more abundant production in those parts. The belief 

 that in trees bled for turpentine a change takes place in the distribution of resin was not sus- 

 tained in the investigations. It was, however, found that the heartwood of old trees contains 

 invariably more oleoresin than the sapwood, the largest amount relatively being found at the line 

 where heart and sapwood join. This would indicate an infiltration of the heartwood witli resin 

 from the sapwood. Before, however, accepting such a conclusion, in which we would find it hard 

 to explain mechanical difficulties in the wandering of the resin, it would be desirable to examine 

 trees of different age and note the progress of resiuification, and also to make further analyses on 



