Inquiries relative to the Structure of Wood. 445 



As one cubic inch of the solid parts of this kind 

 of wood weighs 29.45 grammes,* the 7.1531 

 grammes of ligneous parts found in a cubic 

 inch of the trunk of the living tree, in Sep- 

 tember, could only have occupied the space of 0.24289 cubic inch. 



And the 4.3369 grammes of sap, contained in it, 



only 0.21880 



Consequently, in one cubic inch of this wood 



there was a bulk of air equal to . . . 0.53831 



Total I. ooooo 



The difference between the structure of the oak and 

 of the poplar becomes very conspicuous on making a 

 comparison, according to the subjoined method, between 

 the constituent parts of these two kinds of wood, both 

 in a growing state. 



Thus, a cubic inch of wood is composed of: 



Ligneous parts. Sap. Air. 



The oak . . . 0.39353 0.36122 0.24525 

 The poplar . . 0.24289 0.21880 0.53831 



This striking difference in the proportions of the 

 ligneous substance, of sap, and of air, discovered in these 

 two species, sufficiently explain the difference observable 

 in their weight and hardness. This inquiry may prob- 

 ably lead to other discoveries of more general utility in 

 the study of the vegetable economy. 



SECTION III. Of the relative Quantities of Sap and Air 

 found in the same Tree, in Winter and in Summer ; and 

 in different Portions of the same Tree, at the same Time. 



The following experiments were undertaken with a 

 view to discover the difference between the quantities of 



* See the table, page 440. 



