96 
ORGANOGRAPHY. 
BOOK I. 
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 Scie?ices, 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 
attempts to explain this curious mode of growth upon the sup- 
position that each leaf forms three fascicles of woody matter, 
whereof the central is the most powerful, and produces the 
mass of the stem; and the lateral ones, which are much 
weaker, give origin to the accessory axes ; — and he states, 
that in climbing Sapindaceous plants the same phenomenon 
occurs, only to a far greater extent. He represents that in 
those cases the fibres of each leafstalk separate into three or 
four principal branches, each of which applies itself to one of 
the internal woody axes of the stem, which, in time, consists of 
from four to eight distinct axes, the central being larger than 
the others, and each having its own cortical integument. The 
fact is curious, but I doubt whether the explanation is just. 
(Arch, de BoL, ii. 492.) 
