Day.] 336 [Dee. 21, 
Each of the numbers given in the columns headed, Length of Woody 
Fibre, Exterior Diameter of Woody Fibre and Interior Diameter of 
Woody Fibre is the ave rage of twenty micrometric measurements. The 
numbers in the column headed Duet Area represent the area occupied by 
ducts in one square inch of transverse section, Kach of the results there 
given is the average of planimeter measurement of three camera Jucida 
drawings taken at various parts of a section. 
The results of the first four of the above experiments may be summed 
up thus: A and D stiff hickory and white oak had small annual growth, 
moderately large duct area and moderately thick fibre walls ; whereas B 
and C, elastic hickory and white oak, had moderately large annual growth, 
smal} duct area and thick fibre walls. Whether the general difference 
between elastic and stiff timber is chiefly due to a difference in the char- 
acter of the cellulose, or whether it is chiefly due to a difference of cell 
structure is a question that would require a much more extended series of 
experiments than the above to settle finally. The results given, though 
too few in number to be of great value, point to the latter view of the 
vase ; While the fact that the same piece of wood will, at various ages, ex- 
hibit various degrees of elasticity, inclines us to the former, The experi- 
ments G, J, Jand K show the difficulty of comparing woods of different 
species. For instance, the pieces Gand Jhad almost the same annual 
growth, duct area and fibre thickness. Yet they broke with strains of 
respectively 1750 lbs. and 900 1bs. An observation. that brings out more 
clearly than before the fact that differences of strength in woods of different 
species are largely due to differences in the cellulose, 
The measurements of length of woody fibre given in this and in the 
table of the results of experiments upon the coniferous woods, furnish ex- 
cellent proof of the correctness of the statement made by Dr. Rothrock, 
that the relation between the absolute length of fibre and the strength of 
timber is a very slight one, 
The importance of the medullary ray as a strength giving element, 
though suggested, has not, heretofore, been insisted upon with sufficient 
positiveness. The following experiments, undertaken with reference to 
this point, show that in woods such as Oak and Buttonwood, in which the 
rays are highly developed, a large part of the strength is due to their 
presence. Irom cubes of wood, the edges of which measured six inches, 
plates six inches square and one inch thick were cut in a direction trans- 
verse to the woody fibres. From these, pieces of a Shape suitable for 
testing in a cement testing machine were cut, in such a manner that half 
of the pieces had ‘he medullary rays running in the’ direction in which 
the tension was applied, and half of them in a direction perpendicular to 
this. In each the area subject to strain was one square inch. The result 
gives, of course, the lateral adhesion of the fibres, with and without the 
strength added by the medullary rays. 
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