THE ROOT OF THE ANGIOSPERM 31 
reserve food and the tap roct consequently becomes 
much enlarged. If the swollen tap root tapers to a 
point, as in the carrot, it is called ContvaL; if it is 
swollen in the middle chiefly and tapers at top and 
bottom, as in the radish, it is called Fusiror, if the 
upper part is swollen into the form of a ball, as in the 
case of the turnip, it is called Napirorm. If the whole 
of the tap root becomes spherical it is called PLACENTI- 
FoRM. If a number of slender branches are given off, as 
in grass, the root is Fisrous. When some of the fibres 
are swollen, the term FAscIcULATED is employed. 
19. Branching.—If we examine the root of a fairly 
old plant we notice that the branches of the main or 
tap root are arranged in longitudinal rows, the roots in 
each row being exactly above one another. This is 
owing to the fact that these branches, or secondary 
roots, spring from opposite the xylem, and as the xylem 
runs straight down through the tap root, it follows that 
the bases of the secondary roots will be in a straight 
line. Further, it will be’ noticed that the oldest second- 
ary roots are close to the surface, while at the apex of 
the tap root no branches are to be seen. All root 
branches arise endogenously, i.e. from the interior of 
the main root. The first make their appearance in a 
sheath of cells surrounding the vascular bundles called 
the PrEricycuE (fig. 17). One or more cells of this 
tissue divide and form a mass of new cells—the young 
secondary root. This burrows its way through the 
surrounding cortex and finally breaks out at the surface, 
leaving a distinct cleft to mark its endogenous origin. 
It will be noticed that the tap root grows vertically 
