80 
ORGANOGRAPHY. 
BOOK I. 
tion found in the trunk of the tree, but arranged differently. 
The side next the wood of the parent tree is thicker than the 
opposite side, which Dutrochet attributes to its being more 
immediately in contact with the cambium which nourishes 
it. In the Cedar of Lebanon the nodules have been seen 
producing a small branch from the summit. M. Dutrochet 
regards these nodules as adventitious buds arrested in their 
formation, and he compares them to the internode of Tamus 
communis, which forms a tuberous root-like body in that 
species. 
A circumstance to which this physiologist attaches great 
importance is, that these nodules have an abundance of cam- 
bium in the spring, and yet they are not, he says, in commu- 
nication with the alburnum of the tree ; whence he concludes 
that cambium is elaborated by the bark exclusively. I am not, 
however, able to reconcile this statement (Memoires, i. 311.) 
with another (p. 304.), that the base of the nodule is “cer- 
tainement ” in adhesion with the wood of the tree. 
2. Of its External Modifications. 
It has already been stated, that the first direction taken by 
the stem immediately upon its developement is upwards into 
the air. While this ascending tendency is by many plants 
maintained during the whole period of their existence, by 
others it is departed from at an early age, and a horizontal 
course is taken instead ; while also free communication with 
light and air is essential to most stems, others remain during 
all their lives buried under ground, and shun rather than seek 
the light. From these and other causes, the stems of plants 
assume a number of different states, to which botanists attach 
particular terms. It will be most convenient to divide the 
subject into the varieties of — 
1. The subterranean stem ; and 
2. The aerial stem. 
The SUBTERRANEAN Stem was confounded by all the older 
botanists, as it still is by the vulgar, with the root, to which it 
bears an external resemblance, but from which it is positively 
