1890/ 



MICKOSCOPICAL JOURNAL. 



53 



though possibly it mij^ht have j^reater flexibility. This condition of 

 maturity varies greatly in difl'erent species of tvees as in different 

 shrubs and herbs. Some pass ^'radually on from vouth to decay, while 

 others after attaining their maximum endure for years with little or no 

 change, either in appearance or in the quality of the wood. But as 

 old age approaches in a tree certain signs appear, which an observant 



Georgia pine ( Finns australis). 



lumberman will easily detect. The head of the tree becomes smaller, 

 fewer leaves appear, occasionally a branch drops off, the bark becomes 

 rougher and more covered with moss. With this outward change is a 

 corresponding inner one. The lignification or hardening of the cells 

 advances yearly, until the sap wood is reduced to a thin band only an 

 inch or two thick in a tree three or four feet in diameter. After this there 

 is no profit nor advantage in keeping a tree, and, on the contrary, in 

 short-lived trees a positive loss. 



The most superficial observer of lumber knows that there is generally 

 a considerable difterence between the wood of trees belonging to dificrent 

 species. Sometimes it is quite small, so that lumbermen have no con- 

 stitutional objection to working oft" short leaf for long leaf yellow pine, 

 hemlock for white pine, chittim wood, or yellow cottonwood for poplar 

 and red birch for cherry, if it can be done without detection. The dif- 

 ficulty of distinguishing is greater among the conifers — the pines, spruces, 

 firs, and hemlocks — than among the hardwoods, for the former are all 

 formed on much the same pattern. Fig. i is a specimen of a transverse 

 section of the California sugar pine {Pinns lambertiand) — that is, a 

 section cut cross-ways of the wood as a cucumber is sliced. It, as well 

 as all the other illustrations, is magnified 35 diameters, so that only two 

 rings or circles of yearly growtli are shown. The small cells are nearly 

 square, representing true lignified wood cells, none of the growing cells 



