94 ME. T. HICK OS A NEW FOSSIL PLANT 



(fig. 6, rp). On the outside, this layer, whether its cells 

 become radially arranged or not, passes over without a break into 

 the general parenchyma of the radicular tissues or into a peri- 

 dermal band which abuts on one of the narrow fissures already 

 mentioned (fig. 6, p,f). In these last cases, however, the peri- 

 dium and fissure do not completely surround the other tissues, 

 a portion of which are still in organic connexion with the general 

 parenchyma. 



Though not entirely free from difficulties, the best explanation 

 of the structure of this part of the fossil seems to be that which 

 has been already assumed, viz., that it consists of a number of 

 roots imbedded in a mass of parenchyma from which their peri- 

 pheral tissues are not in all cases or wholly separated. On this 

 view the vascular bundle will represent the axile strand, while 

 the layers of parenchyma which envelope it will represent the 

 inner part of the cortex of a root. The characteristics of this 

 parenchyma are not unlike those usually met with in the inner 

 part of the cortex of recent roots *, a fact which is in favour of 

 the view suggested. 



Longitudinal sections of the specimen, taken tangentially as 

 near the periphery as possible, show that the rootlets emerge 

 approximatively at right angles, and are therefore cut transversely. 

 Seen in such sections, the structure of the roots is not the same 

 in all cases. In some it agrees with that already described in the 

 transverse sections ; but in others it differs, and that in two 

 directions. On the one hand, we have roots with a central col- 

 lateral vascular bundle surrounded by a tissue which is not differ- 

 entiated into layers, and which shows no line of separation from 

 the parent tissues. These roots bear some resemblance to those 

 figured and described by Williamson in his monograph of Stig- 

 maria jicoides, pi. v. fig. 46. On the other hand, we have roots 

 in which the parenchyma round the vascular bundles is sharply 

 differentiated into distinct layers, which give the whole an appear- 

 ance not unlike other rootlets figured and described by Williamson 

 on pi. ix. fig. 51 of the same work. 



Eoots of tbe latter type are nearer the periphery than those of 

 the former, and indeed seem to be on the point of becoming free. 

 As is shown in fig. 7, the tissues which surround the vascular 

 bundle are arranged from within outwards as follows : 



* Van Tieghem, ' Traits de Botanique,' 2nd ed. p. 674. De Bary, ■ Compa- 

 rative Anatomv.' End. ed. do. 404. 412. 



