50 



THE AMERICAK MONTHLY 



[March, 



microscopic examination to ascertain not only the coarseness or fineness 

 of a given specimen, but its elasticity, durability, and adaptation for 

 specific purposes. Trees, like all other vegetable substances, from the 

 green slime that floats on a stagnant pond up to the giant redwood, are 



Fig. 4. — Red fir {Adtes douglasii). 



composed of cells — minute bodies of various shapes and sizes, generally 

 consisting of a sac or membrane filled with fluid or air. Slice a ripe 

 apple or melon, and the cells can easily be seen by the naked eye. The 

 pith of the stem of an elder is composed of simple soft cells. The stem 

 of a cornstalk shows similar cells, and also some of another kind ar- 

 ranged in bundles. The more simple the organization of the plant the 

 more simple the cell structure. As we go higher up in the scale of life 

 — and the rule applies equally to vegetable and animal — the structure 

 grows more complex ; it must be adapted to more varied uses, and 

 hence must have more highly differentiated organs. The fluid in the 

 young, freshly formed cells of plants is called protoplasm, and is the 

 source of all growth. In it the different substances necessary for the 

 growth of the plant are secreted, and when the protoplasm dies the plant 

 dies. The most important element elaborated in tree growth, which forms 

 all the sap wood, part of the heart, and a large portion of the bark is cel- 

 lulose, a familiar example of which, nearly pure, is the common cotton 

 of the well-known cotton plant. Pure cellulose is a white, soft, taste- 

 less substance, insoluble in water or alcohol, and not easily dissolved 

 by weak acids or alkalies. These characteristics are important to be 

 remembered, as on them depend the qualities of different woods. The 

 other chief important element in wood is lignine, which is chemically 

 the same as cellulose, and may be defined as a hardened kind of cellu- 

 lose. It is remarkable for the fact that it is still more inert than cellu- 



