CHAP. 
EXOGENOUS STEMS. 
95 
and many other Myrtaceae, for instance, the zones are ex- 
tremely indistinct ; in some Bauhinias they are formed with 
great irregularity ; and in Stauntonia latifolia, some kinds of 
Ficus, certain species of Aristolochia, as A. labiosa, and many 
other plants, they are so confounded, that there is not the 
slightest trace of annual separation. It is also to be remarked, 
that in Zamias we seldom find more than two or three zones 
of wood, whatever may be the age of the individual ; and yet 
it appears from Ecklon’s observations, that a Zamia, with a 
trunk only four or five feet high, can scarcely be less than two 
or three hundred years old. [Lehm. Pugill. vi.)* 
With regard to judging of the age of a tree by the inspec- 
tion of a fragment, the diameter of the stem being known, a 
little reflection will show that this is to be done with great 
caution, and that it is liable to excessive error. If, indeed, 
the zones upon both sides of a tree w^ere always of the same, 
or nearly the same, thickness, much error would, perhaps, not 
attend such an investigation; but it happens that, from vari- 
ous causes, there is often a great difference between the growth 
of the two sides, and consequently, that a fragment taken from 
either side must necessarily lead to the falsest inferences. For 
example, I have now before me four specimens of wood, taken 
almost at hazard from among a fine collection, for which I am 
indebted to the munificence of the East India Company. 
The measurements of either side, and their age, as indicated 
by the number of zones they comprehend, are as follows : — 
Diameter of 
Total. 
Real 
Side A. 
Side B. 
Age, or 
No. of Zones. 
Benthamia fragifera - 
9 lines. 
36 lines. 
45 lines. 
40 
Pyrus foliolosa - - 
8 lines. 
22 lines. 
30 lines. 
36 
Magnolia insignis - - 
11 lines. 
20 lines. 
31 lines. 
17 
Alnus napalensis - - 
11 lines. 
23 lines. 
34 lines. 
8 
Now, in the first of these cases, suppose that a portion of the 
side A. were examined, the observer would find that each 
* According to Decaisne {Comptes rendus, v. 393.) the zones of wood in 
Menispermacege each result from the growth of several years. 
