VASCULAR CYLINDER. 13 



That the bundles which Goeppert and Binney found in the interior of these 

 Stigmarias were those of Stigmarian rootlets is undoubted, but those rootlets had 

 no individual relationship to the plants in which the two authors found them. 

 They were such as had intruded themselves into the medullary cavity from without, 

 just as they have entered into nearly every fragment of a plant from the Oldham 

 and Halifax deposits, whence most of our rich stores of specimens have been derived. 

 Permeating both the vegetable soil, now converted into coal, and the seat clay, in 

 the most extraordinary profusion, the smallest opening in any part of a vegetable 

 fragment was penetrated by these rootlets, making the study of such specimens 

 extremely perplexing to palaeontologists whose eyes are not familiar with the aspects 

 assumed by these erratic rootlets. Plate VII, fig. 14, g, presents an instance of 

 a rootlet, with its central vascular bundle, /", in the medullary cavity of a Stigmarian 

 vascular cylinder. In Plate X, fig. 42, we have a large rootlet, g, into the interior 

 of which several younger, but otherwise similar, rootlets have penetrated. My 

 cabinet contains another example in which a small rootlet has penetrated a 

 somewhat larger one, and these two, in turn, have entered together into a third 

 of yet larger dimensions. Mr. Binney unfortunately adhered to his error even in 

 his latest writings. 



The Vascular or Xylem Cylinder. 



The transversely barred tubes composing this cylinder belong to the type 

 designated by Brongniart Vaisseaux rayees. They are either vessels or Tracheids 

 (Plate VI, fig. 9, b ; Plate VII, figs. 10, b, and 11, b), assuming the latter form 

 especially where lateral bundles are given off. 



At the earliest appearance of this cylinder in a young root the vessels occupying 

 the position, though not fulfilling the functions, of the protozylem of an exogenous 

 stem, constituted a thin ring of very small vascular bundles surrounding a medulla. 

 These bundles, the vessels of each of which retained their mutual parallelism, did 

 not themselves pursue a straight, longitudinal, but an undulating, course through 

 the stem, as at Plate V, fig. 8, the undulating curves of one bundle being opposed 

 to those of its neighbour on either side. The result of these wavy undulations was 

 that contiguous bundles alternately touched and separated from one another, 

 enclosing, in the latter case, large, vertically elongated, lenticular spaces (fig. 8, b'), 

 occupied by extensions of the medullary parenchyma which thus reached the bark. 

 As the vascular cylinder grew exogenously each new, superadded vessel followed 



the medullary rays, but, as already mentioned, again adopts Goeppert's explanation of the origin of 

 the vascular rootlet bundles." 



3 



