434 VASCULAR CRYPTOGAMS. 



broad base to the stem although it is there really much more slender; but in the 

 upper part there are also a great many roots. In small plants they are very slender; 

 on large plants they attain a diameter of from i to 3 mm. ; they are cylindrical, 

 generally covered with a number of root-hairs which form a kind of felt, and are 

 of a brown or black colour. The history of the growth of Fern-roots has been 

 studied by Nageli and Leitgeb\ The apical cell is a three-sided pyramid, with 

 a convex equilateral base. The segments or layers of the root-cap, detached by 

 convex septa parallel to the base, first divide into four cells placed crosswise, 

 and the walls which effect this division alternate in successive layers by about 

 45°; each of the four cells of a layer then splits up into two external and one 

 internal (central one), so that the layer is now formed of four internal cells 

 arranged in a cross, and of eight external cells. Further divisions may then 

 follow; the central cells of the layer grow more quickly in an axial direction, 

 and may become divided by transverse septa, by which the layer is made to 

 consist of two or more strata in the middle. The formation of a layer of the 

 root-cap is generally followed by that of three root-segments before a further 

 new layer is formed; these segments, corresponding to the faces of the three- 

 sided apical cell, lie in three straight longitudinal rows. Each of these tri- 

 angular tabular segments includes a third of the circumference of the root, and 

 is first divided by a radial longitudinal wall into two unequal portions. The trans- 

 verse section of the root now shows six cells, three of which meet in the centre, 

 while the other three do not reach quite so far. Each of these six cells is then 

 divided by a tangential wall (parallel to the surface) into an inner and an outer 

 cell; the inner ones form the fibro-vascular bundle, while the six outer cells form 

 the rudiment of the cortex. If the root becomes thick, the six cortical cells 

 divide by radial walls: if it remains slender, this division does not take place. 

 The six or twelve cortical cells are now divided by a tangential longitudinal wall, 

 and the fibro-vascular bundle is enclosed by two layers of cells, the outer of 

 which forms the epidermis, the inner the fundamental tissue of the cortex (see 

 Book I, p. 144). 



The roots of Ferns, like those of Equisetaceae, branch monopodially, and 

 the lateral roots arise on the outer side of the primordial fibro-vascular bundles 

 in acropetal succession, usually in two rows, but occasionally in three or four. 

 The cells from which the lateral roots spring belong to the most internal layer 

 of the cortical parenchyma (bundle-sheath), and are opposite to the xylem-bundles : 

 they are separated from the fibro-vascular bundles of the parent root by the 

 pericambium. The rudiments of the roots make their appearance near to the 

 growing-point before the vessels are formed. Adventitious lateral roots, arising 

 behind those which already exist, do not occur. The three-sided pyramidal apical 

 cell is formed in the mother-cell of a lateral root by three oblique septa, and then 

 the first root-cap is produced from it. If two primordial fibro-vascular bundles 

 are developed in the lateral root, they He right and left with reference to the 



^ Sitzungsber. der bayr. Akad. der Wiss. Dec. 15, 1865. Compare with what follows the 

 diagram of a root given under the Equisetacege, which serves in the main also for Ferns and 

 Rhizocarps; also p. 144. [See also Conwentz, Beit, z, Kennt. des Stammskelets einheimischer 

 Fame, Bot. Zeit. 1875.] 



