ROOT, 
167 
fibro-vascular bundle, while in Phanerogams they proceed from the pericambiiim which 
is enveloped by the plerome-sheath (see Sects. 16, 18). In the Cryptogams named 
above the new roots originate each from a single primary mother-cell, and there are 
always particular cells of the plerome-sheath which give rise to the rudiment of a root, 
while in Phanerogams, on the contrary, several of the pericambial cells take part in 
the production of each secondary root. Another difference consists in this, that the 
plane of symmetry of the secondary root is, in Cryptogams, at right angles to that of 
the mother-root, while in Phanerogams (according to Van Tieghem) the two coincide, 
at least when the mother-root and lateral roots each contain only two vascular 
bundles. 
In Ferns, Marsileaceae, and Equisetaceae, where the root developes with an apical 
cell which becomes seg- 
mented on three sides, 
and contributes the cap- 
cells to form the root- 
cap (Sect. 19), the for- 
mation of the lateral 
roots commences with 
cell-divisions, by which 
a three-sided pyramidal 
cell is formed with its 
base outwards, which be- 
haves as the mother-cell 
oftheyoungroot. These 
mother-cells of the la- 
teral roots lie in the 
plerome-sheath of the 
its groups of vessels, 
and are therefore sepa- 
rated from the outer- 
most of these vessels 
by the pericambium. 
Further transforma- 
tions take place sub- 
sequently in the peri- 
cambium, in conse- 
quence of which the 
fibro-vascular cylinder 
of the lateral root co- 
alesces with that of the 
mother-root. This does 
not take place, however, 
in Equisetaceae, where there is no pericambium. 
In Phanerogams it is also the general rule, as has already been mentioned, for the 
lateral roots to originate outside the vascular bundles of the mother-root. An excep- 
tion to this is however, according to Van Tieghem, afforded by Grasses, since these 
have no pericambium exterior to the vascular bundles; the new roots originate there- 
fore on the outside of the phloem-bundles which lie between the vascular bundles and 
exterior to which pericambium occurs. The phenomena are also different in Umbelli- 
ferae and Araliaceae ; a secretion-canal lies here in the pericambium outside each fibro- 
vascular bundle ; and the lateral roots are therefore formed midway between each pair 
of bundles, and therefore outside the phloem-bundle. 
In Phanerogams, according to Reinke, the commencement of a lateral root is 
FIG. 123.— Mode of formation of the lateral roots from a mother-root oiTrapa nataits 
(after Reinke). A the pericambium (tt), bounded by the plerome-sheath r, splits into der- 
matogen [d] and an inner layer which in B is already again divided. C young secondary 
root enclosed in the tissue of the mother-root ; R r cortex of the latter ; tt the pericam- 
bium of the mother-root from which the secondary root has been formed ; h the first 
layer of its root-cap, d its dermatogen. D secondary root in a further stage of develop- 
ment, enclosed only by the plerome-sheath r of the mother-root ; p p lis periblem, 
within which is the plerome m m. 
