Envelop 



FROM THE LOWER COAL-ME4SUEES. 91 



Lying outside the 



entire series of structures hitherto described is an enormously 

 thick mass of tissues, the various parts of which are certainly not 

 equivalent to one another, either in histological character or in 

 origin and development. Their massiveness is indicated by the 

 fact already mentioned, that the total diameter of the specimen 

 is nine times that of the vascular-bundle ring. 



At a distance of a few millimetres from the extreme edge of 

 the transverse section there runs an undulating line roughly 

 parallel to it, which marks a difference of histological structure 

 between the tissues on the inner and outer side of it (fig. 2, I). 

 At two points on one side of the section shown in these figures 

 the outer tissue dips down into the inner mass for some distance, 

 and is traceable in one case as a narrow band nearly up to the 

 peri cycle (fig. 2, i). On the other hand, the inner tissues 

 send out several short prominences into the outer zone, and this 

 appears to have some relation to vascular bundles which lie at 

 their distal ends (fig. 2, c). 



On the ground of the facts observed in the various sections 

 and of the histological structure of the whole, I am disposed to 



d) 



? 



and the more massive tissues lying between it and the pericycle as 

 something intercalated by secondary developments. Imbedded 

 in these latter we find numerous root-like structures, which are 

 either organically connected by the parenchyma in which they 

 lie, or are separated by extremely narrow fissures. Hence we 

 shall find it convenient to speak of the whole of the enveloping 

 tissues as being composed of true cortex and radicular tissues. 



The True Cortex forms a narrow zone at the circumference of 

 the transverse section (fig. 2, d). The outer periphery is so 

 ill-defined that its identity with the epidermis is doubtful, and 

 rather suggests that the superficial layers have disappeared. It 

 is cellular throughout, and even to the naked eye has a different 

 appearance from the radicular tissues. 



Where the peripheral part is best preserved, the following 

 layers are distinguishable as we pass from without inwards : 



i. A layer 5 or 6 cells deep, whose elements are arranged in 

 tangential series, and are slightly elongated in the same direction, 

 having an average size of 0*085 millim. by 0*0425 millira. 

 (fig. 2, a). 



ii. A layer apparently 3 cells deep, whose lumina are for the 



