RESIX CANALS IN WHITE FIR 



351 



No doubt some of this water from 

 the fields did, as surface water, aid in 

 the temporary restoration of our springs 

 and wells. 



From March i until April 17 we had 

 (in Chester County, Pennsylvania) but 

 little rain. (The West Chester record 

 kept by Doctor Green shows but 1.37 

 inches.) 



The country was again sufifering 

 from drought. Farming operations 

 were delayed because of the condition 

 of the soil. Complaints were again 

 heard because of shortage of water. 

 The relief obtained from the surface 

 flow in the last of February was ceas- 

 ing. It is fair to say that jirobably most 

 of the water available just prior to the 



bountiful rains of the middle of April 

 came from our forest ground storage. 



Where the leaves and humus on the 

 forest floor have been destroyed by fire 

 the ground freezes, just as it does in 

 the open field. 



I am aware that there come times 

 when the ground freezes in the forests 

 as well as elsewhere, but I also know 

 that in our Central States this is the 

 exception rather than the rule. 



Mr. Moore could not have been ig- 

 norant of facts like these, and of their 

 bearing upon the question he was dis- 

 cussing, but the wonfler is that he did 

 not make sjx'cific allusion to them in 

 so extended a jjaper as "The Influenct^ 

 of Forests on Climate and on Floods." 



THE HISTOLOGY OF RESIN CANALS IN 



WHITE FIR 



By C. D. MELL, Assistant Dendrologist, Forest Setvice 



IXTkODUCTION 



IN CLASSIFYING the woods of 

 conifers by their structural char- 

 acters, they are usuaFy divided 

 into two groups ; first, those that 

 contain resin canals in the sec- 

 ondary wood, and, second, those in 

 which resin canals are wanting. x'Vll 

 conifers so far investigated have resin 

 passages or resin sacs in their leaves, 

 bast, or primary wood. Finns, Picea, 

 and Larix are usually regarded as the 

 onl}- ones that have resin canals in the 

 secondary wood of both stems and 

 roots. Von MohP states that resin 

 canals are not present in the wood of 

 white fir, Abies pectinata D. C, while 

 Schacht- declares that resin canals are 

 wholly wanting in the wood of all spe- 

 cies of Abies. Following the announce- 

 ment of these observations, DippeF 



^Bot. Ztg.. i860. No. 30, page 3:^7. 

 'Bot. Ztg., 1862, Nos. 48 and 49. 

 'Dot. Ztg., 1863, No. 35, page 253. 



studied numerous samples of wood of 

 white fir from trees grown under dif- 

 ferent soil and climatic conditions. The 

 san:plcs were taken from different parts 

 of trees thirty to 100 years of age. 

 With these samples Dippel proved con- 

 clusively that resin canals are not en- 

 tirely wanting in white fir ; that they 

 occur less frequently than in the wood 

 of pine, spruce, and larch. The isolated 

 wood-parenchyma cells are invariablv 

 associated with the production of resin, 

 and for this reason are termed resin 

 cells ; when they enter into the composi- 

 tion of compact groups of cells leading 

 to the organization of secretory passage 

 they are termed resin canals. 



The building of resin in these pass- 

 ages is dependent upon the starch in 

 surrounding wood-parenchyma fibers, 

 but it must net be taken for granted 

 that all starch is consumed in the for- 

 mation of resin, for a great deal is used 

 in other processes. The origin of resin 

 in resin canals is the same as that in 

 small groups of resin cells. As has al- 



