356 AMERICAN FORESTRY 



are replaced by a fluid mass which is eids, and invariably contain resin in old 



further transformed into resin. A com- wood. 



parative study of resin passages in 2. Large Groups of Resin Cells. 

 young and old parts of stems shows that Large groups of elongated wood- 

 there is no visible change in the cell- parenchyma fibers containing resin are 

 walls while the resin hardens. Careful invariably surrounded by elements that 

 measurements also show that the walls may or may not contain resin in the 

 do not diminish in thickness whatso- older parts of the wood, 

 ever, whether the resin is merely de- 3. Resin Canals. True resin canals 

 posited in thin layers or whether the are always surrounded by wood- 

 cavities are completely filled. parenchyma fibers that are invariably 

 In the large groups of resin cells, the in communication with pith rays and 

 behavior is similar to that in the small contain starch. 



groups. The entire parenchymatous The investigation also shows, first, 

 tissue in the younger parts of the ulti- that resin in the white fir originates in 

 mate twigs is filled with starch. In the wood-parenchyma fibers and that it 

 the older twigs the cells toward the never occurs normally in tracheids ; 

 inner part of the stem are filled with second, resin is developed by the con- 

 resin, while the wood-parenchyma cells version of starch in wood-parenchyma 

 surrounding them are filled with starch fibers ; third, that true resin canals are 

 during the winter, and during the sum- developed by the disorganization of cell- 

 mer contain a liquid resembling tur- walls prior to the hardening of resin ; 

 pentine. The starch yields material for and fourth, that the formation of resin 

 the manufacture of resin. Similar con- canals must not be considered as a 

 ditions are present in the older wood, cause, but as a result of resin develop- 

 The resin mass eventually becomes so ment. 



hard that it may be removed from the EXPLANATION OF FXGURES 

 canal without breaking it (Fig. 4). 



There is a continued increase of , The illustrations are magnified 280 diam- 



,, r i 1 i i_ eters and are slight modifications of those 



resin mass in the cells of old wood by given by Dippel in Botanishe Zdtung, 1863, 



the conversion of starch cells into resin p. 253. The abbreviations used with these 



cells. This is shown by the fact that figures are as follows: r. c., resin cells; 



old wood contains more resin cells than st c " st . arch cells; st - starch granules; 



A , r. p., resin passage ; p. r., pith rav 



younger wood. A comparative mvesti- Fig . ,. Transverse section showing a small 

 gation, however, affords no definite in- group of resin cells partly filled with a semi- 

 formation as to when this process fl uid . mass. 



ceases. ^ l &- 2 - Longitudinal radial section showing 



^PI " , , . . r cells of a wood-parenchyma fiber containing 



I he origin of the resin is, therefore, starch granules. 



dependent upon the conversion of Fig. 3. Transverse section showing a larger 



starch into a fluid mass resembling tur- g ro "P of resin cells just inside thick walled 



pentine. Later it is diffused from the ira hdds f th f ] ate , wo ,. d - 



,, ., rig. 4- Longitudinal radial section showing- 

 outer into the inner cells, where it un- hardened resin in resin canal. 



dergoes further change and is con- Fig. sA. Longitudinal radial section show- 

 verted into resin. The normal increase m S resin passage with certain cells partly 

 of resin is, therefore, supplied by the fi V w % re | n ' 



surrounding starch cells. The new sup- pa f s ?ge. 5 * ^ 

 ply of converted starch always passes Fig. 6. Transverse section of a resin pass- 

 on toward the inner cells of the group a g e among the thin walled tracheids of the 



for the formation of resin. ea ^7 w00 ^- 



np-i, i . , , , . rig. 7- transverse section of a resin pass- 



L-he conclusions derived from this ag e in a young twig prior to the formation 



investigation are that the resin-contain- of resin. 



ing elements in the wood of white fir Fig " 8 ". Longitudinal radial section of resin 



i .. . passage in young twig prior to the formation 



can be conveniently grouped as follows : O f resin. 



I. Resin Cells. Wood-parenchyma Fig- 9- Longitudinal radial section of a 



fibers (Hartig's cell-fibers) are usually r ?f n P assa ^ e ' showing partially dissolved 



,, . side and cross walls of the original resin 



scattered among the thin-walled trach- cells. 



