96 PROCEEDINGS OF THE AMERICAN ACADEMY 



in consideration of the greater thickness of the layers as a younger 

 tree ? The only direct data I possess bearing on this point are derived 

 from a piece of a transverse section, 3| inches deep, of a ' rail ' 

 which the exhibitor says was taken from the trunk at the height of 

 275 feet from the ground. As its layers, on a breadth of nearly 

 seven eighths of an inch, show only a slight perceptible curvature, it 

 must have come from a part of the trunk still of several feet in di- 

 meter. On this section the exterior inch, nearly all alburnum, con- 

 tains 90 layers ; the next, 60 ; the next, 45 ; the remaining half-inch, 

 16, making 32 to the inch. That the exterior layers should be thin- 

 ner at this height than those near the base of the tree, is just what 

 would be expected. If we apply this ratio of decrease of the num- 

 ber of layers to the inch as we proceed inwards, to the section at 

 twenty-five feet from the ground, we should, at four inches within 

 that part of the circumference which I have examined, have only 

 17 layers to the inch, which, taken as the average thickness, would 

 make the tree only 1034 -|- 24 = 1058 years old. But it is not 

 probable that the thickness of the layers increases so rapidly. The 

 data we possess on other trees go to show that a tree, after it is 400 or 

 500 years old, increases in diameter at a pretty uniform rate for each 

 twenty additional years, on the whole, although the difference in the 

 thickness of any two or more contiguous layers, or of the same layer 

 in different parts of the circumference, is often very great. Still, 

 when we consider how very much thicker are the annual layers of a 

 vigorous young than of an old one, perhaps we should not be war- 

 ranted in assuming more than the average of 17 layers to the inch 

 for the whole section. 



" Some useful data may be obtained from a tree more nearly re- 

 lated than any other to the two California ones, though of a different 

 genus, namely, the so-called Cypress of our Southern States ( Taxodium 

 distichum). I possess three sections of different trees of Taxodium, 

 reaching from the centre to the circumference. One of these, on an 

 average radius of 27 inches, exhibits 670 layers ; a second, on a 

 radius of 30 inches, has 525 ; a third, on a radius of 22 inches, has 

 534 layers. The average is 576 layers to a semidiameter of 26 

 inches, or about 22 layers to an inch. Half of this growth (13 inches 

 radius) was attained at the close of the first century ; while the ex- 

 terior layers of the oldest specimens were only the fiftieth or sixtieth 

 of an inch in thickness. We have reason to believe, therefore, that 



