360 HOFME1STER, ON 



The position of the vascular bundles of the roots remains 

 throughout the whole life of the plant the same as in the 

 first year : they are always brought close to that side of the 

 root which is turned towards the indentation of the stem. 

 The cambial cells between the places of origin of those 

 vascular bundles which pass to the new roots become for 

 the most part woody : individual cells only, situated between 

 the transformed annular and spiral cells, remain thin-walled 

 (PL LII, fig. 6). Thus the latterally compressed lower half 

 of the woody mass grows downwards at its convex edge, at 

 the same time increasing in diameter. 



The roots of Isoetes usually ramify in a furcate manner 

 repeatedly as many as four times during their longitudi- 

 nal development.* Judging from the arrangement of the 

 cells of roots which have only just become forked, it would 

 seem that the furcation commences with the longitudinal 

 division of the cell of the first degree of the apex of the root, 

 by means of a septum at right angles to the larger trans- 

 verse diameter of the downward-growing wood (PI. LII, fig. 

 2). The forks of the roots separate from one another at an 

 angle of about 30; the tw T o first are parallel to the furrow 

 of the stem. The direction of the next ramifications differs 

 by about 90 from the former. The excentrical vascular 

 bundles of the forks of the root are always removed to that 

 side which is turned towards the sister-fork of the root 

 (PL LII, fig. 3). 



Every year the same processes are repeated. The old 

 bark is thrown off and replaced by new. The upper cylin- 

 drical portion of the wood grows upwards by the lignification 

 of those cells of the terminal bud which overlie its summit, 

 and by the addition of the rudiments of vascular bundles 

 intended for the new roots. Its half-moon-shaped lower 

 portion increases in circumference on the convex edge, by 

 the addition of the bases of the vascular bundles which 

 jmss to the new roots. Thus the plant becomes continually 

 more vigorous ; the number of the leaves and roots increases 

 in each new vegetative period. 



The abundant development of leaves, in connexion with 



* Discovered by Alexander Braun in 1847. ' Flora,' p, 33. 



