CHAP. III. 
ORIGIN OF WOOD. 
267 
ing sap. The first of these opinions appears to be that of 
Turpin, as far as can be collected from a long memoir upon 
the grafting of plants and animals. The second is the opinion 
commonly entertained in France, and adopted by De Candolle 
in his latest published work. 
The objections to the views of Turpin need hardly be 
stated. Those which especially bear upon the view taken by 
De Candolle are, that his theory is not applicable to all parts 
of the vegetable kingdom, but to exogenous plants only ; that 
it is inconceivable how the highly organised parallel tubes of 
the wood, which can be traced anatomically from the leaves, 
and which are formed with great rapidity, can be a lateral 
deposit from the liber and alburnum ; that they are manifestly 
formed long before it can be supposed that leaves have 
commenced their office of elaborating the descending sap; 
and, finally, that endogens and cryptogamic plants, in which 
there is no secretion of cambium, nevertheless have wood. 
Such is the state of this subject at the time I am writing. 
To use the words of De Candolle, " The whole question may 
be reduced to this — Either there descend from the top of a 
tree the rudiments of fibres, which are nourished and deve- 
loped by the juices springing laterally from the body of wood 
and bark ; or new layers are developed by pre-existing layers, 
which are nourished by the descending juices formed in the 
leaves." 
As this is one of the most curious points remaining to be 
settled among botanists, and as it is still as much open to 
discussion as ever, I have dwelt upon it at an unusual length, 
in the hope that some one may have leisure to prosecute the 
inquiry. Perhaps there is no mode of proceeding to eluci- 
date it which would be more likely to lead to positive results, 
than a very careful anatomical examination of the progres- 
sive development of the mangel wurzel root, beginning with 
its dormant embryo, and concluding with the perfectly formed 
plant. 
