356 



AMERICAN FORESTRY 



are replaced by a fluid mass which is 

 further transformed into resin. A com- 

 parative study of resin passages in 

 young and old parts of stems shows that 

 there is no visible change in the cell- 

 walls while the resin hardens. Careful 

 measurements also show that the walls 

 do not diminish in thickness whatso- 

 ever, whether the resin is merely de- 

 posited in thin layers or whether the 

 cavities are completely filled. 



In the large groups of resin cells, the 

 behavior is similar to that in the small 

 groups. The entire parenchymatous 

 tissue in the younger parts of the ulti- 

 mate twigs is filled with starch. In 

 the older twigs the cells toward the 

 inner part of the stem are filled with 

 resin, while the wood-parenchyma cells 

 surrounding them are filled with starch 

 during the winter, and during the sum- 

 mer contain a liquid resembling tur- 

 pentine. The starch yields material for 

 the manufacture of resin. Similar con- 

 ditions are present in the older wood. 

 The resin mass eventually becomes so 

 hard that it may be removed from the 

 canal without breaking it (Fig. 4). 



There is a continued increase of 

 resin mass in the cells of old wood by 

 the conversion of starch cells into resin 

 cells. This is shown by the fact that 

 old wood contains more resin cells than 

 younger wood. A comparative investi- 

 gation, however, affords no definite in- 

 formation as to when this process 

 ceases. 



The origin of the resin is, therefore, 

 dependent upon the conversion of 

 starch into a fluid mass resembling tur- 

 pentine. Later it is diffused from the 

 outer into the inner cells, where it un- 

 dergoes further change and is con- 

 verted into resin. The normal increase 

 of resin is. therefore, supplied by the 

 surrounding starch cells. The new sup- 

 ply of converted starch always passes 

 on toward the inner cells of the group 

 for the formation of resin. 



The conclusions derived from this 

 investigation are that the resin-contain- 

 ing elements in the wood of white fir 

 can be conveniently grouped as follows : 



I. Rcsi}i Cells. — Wood-parenchyma 

 fibers (Hartig's cell-fibers) are usually 

 scattered among the thin-walled trach- 



eids, and invariably contain resin in old 

 wood. 



2. Large Groups of Resin Cells. — 

 Large groups of elongated wood- 

 parenchyma fibers containing resin are 

 invariably surrounded by elements that 

 may or may not contain resin in the 

 older parts of the wood. 



3. Resin Canals. — True resin canals 

 are always surrounded by wood- 

 parenchyma fibers that are invariably 

 in communication with pith rays and 

 contain starch. 



The investigation also shows, first, 

 that resin in the white fir originates in 

 the wood-parenchyma fibers and that it 

 never occurs normally in tracheids ; 

 second, resin is developed by the con- 

 version of starch in wood-parenchyma 

 fibers ; third, that true resin canals are 

 developed by the disorganization of cell- 

 walls prior to the hardening of resin ; 

 and fourth, that the formation of resin 

 canals must not be considered as a 

 cause, but as a result of resin develop- 

 ment. 



EXPLANATION OF FIGURES 



The illustrations are magnified 280 diam- 

 eters and are slight modifications of those 

 given by Dippel in Botanishe Zcitung, 1863, 

 p. 253. The abbreviations used W\Xh these 

 figures are as follows : r. c, resin cells ; 

 St. c, starch cells ; st. g., starch granules ; 

 r. p., resin passage; p. r., pith ray. 



Fig. I. Transverse section showing a small 

 group of resin cells partly filled with a semi- 

 fluid mass. 



Fig. 2. Longitudinal radial section showing 

 cells of a wood-parenchyma fiber containing 

 starch granules. 



Fig. 3. Transverse section showing a larger 

 group of resin cells just inside thick walled 

 tracheids of the late wood. 



Fig. 4. Longitudinal radial section showing 

 hardened resin in resin canal. 



Fig. 5A. Longitudinal radial section show- 

 ing resin passage with certain cells partly 

 filled with resin. 



Fig. 5B. Transverse section of a resin 

 passage. 



Fig. 6. Transverse section of a resin pass- 

 age among the thin walled tracheids of the 

 early wood. 



Fig. 7. Transverse section of a resin pass- 

 age in a young twig prior to the formation 

 of resin. 



Fig. 8. Longitudinal radial section of resin 

 passage in young twig prior to the formation 

 of resin. 



Fig. 9. Longitudinal radial section of a 

 resin passage, showing partially dissolved 

 side and cross walls of the original resin 

 cells. 



