ROOT, 



167 



fibro-vascular bundle, while in Phanerogams they proceed from the pericambium 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 v/hich 

 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 

 axial bundle, in front of 

 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 thes2 

 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 of Trapa ttatans 

 (after Reinke). A the pericambium (tt), bounded by the plerome-sheath r, splits into der- 

 matogen [d) and an inner layer n, 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; It 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 ; / > its periblem, 

 within which is the plerome ;« m. 



