1890.] 



MICKOSCOPICAL JOURNAL. 



51 



lose, particularly to the action of water. Now, the character of a tree 

 depends very largely on the proportion of cellulose and lignine, and this 

 can be determined to a great degree by chemical reactions made on 

 specimens of wood under the microscope. If a tree is nearly all cellu- 

 lose the w^ood will be light-colored or white, soft, easy to split, and 

 quick to decay, and very liable to swell or shrink with changes of 

 weather. The tree will generally be short-lived, and will prefer moist, 

 alluvial soil. The lignified tissue is the product of age and a certain 

 degree of dryness, and is found in the highest degree in slow-growing 

 trees, raised on high land or on a sandy loam. Other things being 

 equal, the value of a hardwood tree is in direct proportion to the amount 

 of lignified tissue it contains, though there must be some cellulose still 

 remaining, or the wood will be brittle. 



Though there are many varieties of cell structure, depending on the 

 kind of tree and its mode of growth, there are only three or four which 

 it is necessary to consider here. 



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h iG. 5. — Redwood {Segtinia senipervirens). 



The first formed are soft, thin-walled, nearly globular bodies, about 

 i-3ooth to i-i5oth of an inch in diameter, growing rapidly by division 

 and containing a large amount of fluid. These gradually become 

 changed by mutual pressure into prismatic or elongated forms, and 

 with the alteration in form comes a change in the part the cells perform 

 in the development of the plant. It must be remembered that this cell 

 structure is not due to an aggregate of individual independent organisms 

 assembled together like a colony of bees, but it is one integral whole made 

 up of innumerable parts, controlled by some influence which is termed 

 the law of growth or law of development, so that a cherry pit never 

 develops into an apple, nor a walnut into an oak. The second or 



