24 STIGMARIA FICOIDES. 



enlarged, are taken from Mr. Ward's large Staffordshire vascular cylinder, on the 

 periphery of which similar wedge-shaped bundles are numerous. 1 



As we have already seen, each of these rootlet bundles originates, when the root 

 is in its youngest state, as a single very small vessel, the dimensions of which 

 bear a ratio to those of the young cylinders whence it emanates. In like manner, 

 as the vessels of the newer additions to that cylinder increase in size, such portions 

 of those additions as enter into the formation of the pre-existing rootlet bundles 

 do the same. Yet after many such additions have been made, and the bundle has 

 attained to relatively large dimensions, we not unfrequently find, added to its broad 

 base, and especially to its two basal corners, a few vessels, the diameters of which 

 are little more than those (/') of what may be called the protoxylem of the bundles. 

 Such additions are seen at/, Plate IV, fig. 31. As already pointed out, these 

 later additions are derived from new and half-developed zones that are being added 

 to the exterior of the vascular cylinder, as represented in Plate IV, fig. 19, b'. 

 We shall find that similar conditions, due to similar causes, reappear after these 

 bundles have escaped from the cortex and constitute the central structures of the 

 actual rootlets. 



As to the regularity of their radial arrangement, to which M. Renault attaches 

 so much importance, the vessels composing these bundles, whilst they are passing 

 through the bark, exhibit a considerable variability. Plate IV, fig. 28, on the one 

 hand, Plate IX, fig. 35, and Plate XI, fig. 36, on the other, illustrate this state- 

 ment. Yet that all these figures, including their innumerable intermediate modi- 

 fications, are but vegetative repetitions of the same organ, is certain. 



Plate XII, fig. 37, is a fragment of a Stigmaria, split vertically, which has revealed 

 the exterior of the vascular cylinder at 6, whilst the rootlet bundles, /, escaping 

 successively from that cylinder, bend downwards and outwards. This is the only 

 specimen I have obtained which demonstrates the regularity of this arrangement. 



Plate XII, fig. 38, is one end of a portion of the vascular cylinder of a specimen 

 exactly resembling fig. 40, from Mr. Bayles' brickyard near Leeds, and for which 

 I am indebted to Professor Green, of the Yorkshire College of Science. Primarily 

 they and others were derived from below the Crow Coal. The medullary cavity 

 of fig. 38 is occupied excentrically by a large intruded Stigmarian rootlet with its 

 conspicuous vascular bundle. Fig. 39 is a lateral view of the same specimen. Both 

 these figures are of the natural size. On the exterior of fig. 39 we see numerous 

 rootlet bundles,/, escaping from the periphery of the cylinder in a regular order, 

 disturbed only by the circumstance that, the inner cortical zones having disappeared, 



1 On various occasions M. Eenault has affirmed that there are two distinct classes of these 

 bundles, which he illustrates by Plate xx, figs. 1, 2, 3 of his ' Cours de Botanique fossile,' premiere 

 annee. He says that whilst his wedge-shaped bundle, fig. 1, has supplied a leaf, figs. 2 and 3 are the 

 bundles of rootlets. The absence of all foundation for this distinction will be discussed on a later 

 page. 



