86 
ORGANOGRAPHY. 
BOOK !• 
appendages ; neither do they ever indicate upon their surface, 
by means of scars, any trace of such : all underground bodies 
upon which scales have been found are stems, whatever they 
may have been called ; the only appendages roots ever have 
are such things as the little hollow floating bladders found in 
Utricularia. A fourth distinction between roots and stems is, 
that the former have never any stomates upon their cuticle ; 
and, finally, in Exogens the root has never any pith. It has 
been also said that roots are always colourless, while stems are 
always coloured ; but aerial roots are often green, and all un- 
derground stems are colourless. 
The body of the root is sometimes called the caudex ; the 
minute subdivisions have been sometimes called radicules, — a 
term that should be confined to the root in the embryo; 
others name them Jihrils^ — a term more generally adopted ; 
while the terms rliizina and rliizula have been given by Link 
to the young roots of mosses and lichens. 
A Jlhril is a little bundle of annular ducts, or sometimes of 
spiral vessels, encased in woody fibre, and covered by a lax 
cellular integument: it is in direct communication with die 
vascular system of the root, of which it is, in fact, only a sub- 
division ; and its apex consists of extremely lax cellular tissue 
and mucus. This apex has the property of absorbing fluid 
with great rapidity, and has been called by De Candolle 
the Sjyongiole or SpongeleL It must not be considered a par- 
ticular organ ; it is only the newly formed and forming tender 
tissue. In Pandanus the spongelets of the aerial roots consist 
of numerous very thin exfoliations of the epidermis, which 
form a sort of cup fit for holding water in. 
The proportion borne by the root to the branches is ex- 
tremely variable: in some plants it is nearly equal to them, 
in others, as in Lucerne, the roots are many times larger and 
longer than the stems ; in all succulent plants and in Cucur- 
bitaceae they are much smaller. When the root is divided into 
a multitude of branches and fibres, it is called fibrous : if the 
fibres have occasionally dilatations at short intervals, they are 
called nodidose. When the main root perishes at the extremity, 
it receives the name of pj'cetnorse, or bitten off*: frequently it 
consists of one fleshy elongated centre tapering to the ex- 
