CHAP. V. 
ORIGIN OF WOOD. 
319 
Hence a plant is formed of multitudes of buds or fixed 
embryos, each of which has an independent life and action : 
by its elongation upwards forming new branches and con- 
tinuing itself, and by its elongation downwards forming wood 
and bark ; which are therefore, in Du Petit Thouars’s opinion, 
a mass of roots. 
This opinion would probably have been more generally 
received, if it had not been too much mixed up with hypothe- 
tical statements, to the reception of which there are, in the 
minds of many persons, strong objections ; as, for example, 
that mentioned in the last paragraph. The theory, never- 
theless, seems better adapted than any other to explain the 
cause of the many anomalous forms of exogenous stems which 
must be familiar to the recollection of all botanists; and it is 
equally applicable to the exogenous and endogenous modes 
of growth, a condition which, it will be readily admitted, is 
indispensable to every theory of the formation of wood. 
In the most recent days, it has had the advantage of being 
supported by M. Gaudichaud, who has made, it is said, a 
great number of very important and interesting observations 
upon the developement of stems. But, as the Memoir of this 
learned botanist is still unpublished, little is known of the 
manner in which he has treated his subject : the best account 
of it is given in the sixth edition of Achille Richard’s Nouveaiix 
E'Umens de Botanique, p. 167. So far as I am able to under- 
stand the short statement there made, the principal peculiarity 
in M. Gaudichaud’s views consists in his assigning the growth 
of plants to a sort of polarity produced by the action of two 
opposite systems, of which the one, or ascending^ consists of 
trachenchyma exclusively, the other, or descending, of bothren- 
chyma and pleurenchyma. It does not appear to which system 
the parenchyma is assigned ; the line of demarcation between 
them is called the mesocauleorhiza* The leaf would appear to 
be regarded as a form of stem divided into three parts, of 
which the lowest is the internode from which the leaf 
emanates, the middle the petiole, the upper the lamina. The 
line of demarcation between the internode and petiole is 
called the mesophytum ; that between the lamina and petiole 
the mesophyllum. It is however impossible to form any opi- 
nion concerning this theory in the absence of the evidence 
