I0 INTRODUCTION 



First. Those resulting from the Uniied States Forestry 

 Bureau Experiments noted in the preceding article and which, 

 so far as they exist, occupy the leading spaces directly under 

 the titles. 



Second. Those conducted at the Water town Arsenal by Mr. 

 Sharpless for the tenth United Stales census and mentioned in 

 item 2, pages 8 and 9. These appear in the second spaces, 

 that is, in lines immediately following those occupied by or set 

 apart for the Forestry figures or their equivalents. 



All coefficients are in pounds per square inch; fractions of 

 pounds in weight and lower figures in coefficients have been' 

 omitted as superfluous. 



It is not always easy to determine the species of living 

 trees, because forms in the forest differ from those in the open, 

 because bark varies with age, and because fruit and leaves of 

 many trees are lacking in the winter. It is easier to tell 

 genus than species that a tree is an oak, than whether it is a 

 red or a pin oak. Experience is required in this connection. 



It is also hard to identify many woods. Colors and appear- 

 ances vary and are hard to describe. Artisans become familiar 

 with a few kinds of woods, but they are usually uncertain with 

 regard to others. The key suggested by Professors Fernow 

 and Roth (Bulletin 10, U. S. Forestry Bureau, pages 59-83), 

 should be referred to. The sections prepared by Hough are 

 very valuable. The Jesup Collection is available to those 

 living near New York City. 



Trees are divided according to the manner in which new 

 material is added to the section. This is sometimes on the 

 outside of older growth and next to the bark or else it is inside 

 distributed over the section. Woods are correspondingly dis- 

 similar, and the two general divisions into which trees are thus 

 separated are known as Exogens and Endogens.* 



* This division coincides with that by which they are separated into Dicotyle- 

 dons and Monocotyledons. It applies to all higher organized plants. 



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