CHAP. II. 
EXOGENOUS STEMS. 
75 
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 Compan3^ 
The measurements of either side, and their age, as indicated 
by the number of zones they comprehend, are as follows : — 
Diameter of 
Side A. j Side B. 
Total. 
Real 
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 - - 
1 1 lines. 
20 lines. 
31 lines. 
17 
AlniJs napalensis - - 
1 1 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 
zone is 0-225 of a line deep ; and, as the whole diameter of 
the stem is 45 lines, he would estimate the side he examined 
to be 22*5 lines deep ; consequently, he would arrive, by cal- 
culation, at the conclusion, that, as his plant was one year 
growing 0*225 of a line, it would be a hundred years in 
growing 22*5 lines, while, in fact, it has been only forty years. 
And so of the rest. 
When we hear of the Baobab trees of Senegal being 5150 
years old, as computed by Adanson, and the Taxodium dis- 
tichum still more aged, according to the ingenious calculations 
of Alphonse De Candolle, it is impossible to avoid suspecting 
that some such error as that just explained has vitiated their 
conclusions. 
To the characters above assigned to the stem of Exogenous 
plants there are several remarkable exceptions, some of which 
have been described by botanists ; others are mentioned now 
for the first time. 
Mirbel has noticed the unusual structure of Calycanthus 
(Annales des Sciences, vol. xiv.), in the bark of which, at equal 
distances, are found four minute extremely eccentrical woody 
axes, the principal diameter of which is inwards ; that is to say, 
next the wood. The existence of this structure, noticed by 
the discoverer only in C. floridus, I have since ascertained in 
all the other species, and also in Chimonanthus. Gaudichaud 
