26 STIGMARIA FICOIDES. 



Plate X, fig. 43, Plate VI, fig. 45, and Plate VIII, fig. 15, alike show that the 

 parenchymatous layer g" and g of Plate X, fig. 42, is a cylindrical extension of the 

 outermost parenchyma, d, of the cortex of the root. The exact sources whence 

 some of the more internal layers of the rootlets were derived is less easily 

 determined, owing to our not having yet succeeded in tracing any bundles, in 

 unbroken continuity, from the point of emergence from the vascular cylinder to 

 the periphery of the bark. 



No one of the numerous sections of rootlet bundles, made, like figs. 28 to 33, 

 Plate IV, close to the vascular cylinder whence those bundles have just issued, 

 shows any definite indications of being enclosed in a special bundle cylinder, such 

 as invests each one when it reaches the base of a rootlet. Yet the rounded contour 

 of the similar bundles of fig. 39, Plate XII, suggests that they must have possessed 

 such an investment. "We recover the interrupted continuity of the bundles at 

 Plate X, fig. 43,/, and Plate VI, fig. 45, /, at which point each bundle penetrates 

 a specialized tissue upon which every rootlet is planted. This tissue forms a short, 

 broad, cellular cylinder, h, which I would designate the rootlet cushion. It is 

 composed of innumerable parallel rows of yery small cells, arranged radially, 

 which pass outward through the prosenchymatous zone, d', of the bark, and extend 

 into the interior of each rootlet, within which they terminate in a conical projection, 

 as in Plate VIII, fig. 15, h, Plate X, fig. 44, h', and Plate VI, fig. 45, h'. In some 

 instances, as in Plate X, fig. 43, h, its radial lines of cells describe complex curves. 

 In the latter figure, as also in fig. 45, we find the vascular bundle entering the 

 base of the cushion at /. In Plate VI, fig. 45, the bundle is unquestionably 

 encased in a small cylinder of delicate cells,/", which are elongated parallel to the 

 bundle. In the specimen Plate X, fig. 44, the outer portion of the bundle,/ the 

 basal part of which is similarly, though less conspicuously, invested, has entered 

 the interior of the rootlet, as is also the case with tbe corresponding bundle of the 

 central rootlet of Plate VIII, fig. 15. 



A tangential section of the bark, crossing a rootlet cushion transversely, as in 

 Plate V, figs. 46 and 47, reveals a mass of very small parenchymatous cells, h, with 

 the vessels of the rootlet bundle in their centre at / In some such sections 

 these cells are distinguished with difficulty from the vessels. The figures of the 

 above sections are enlarged twenty diameters. In Plate V, fig. 48, in which the 

 centre of fig. 46 is further enlarged to 200 diameters, the vessels are seen at /, whilst 

 a small vacant space at/ looks as if it had been occupied by the phloem portion of 

 the vascular bundle. Surrounding the cells, figs. 46 and 47, h, we have a zone, h\ 

 composed of rather larger cells. In fig. 47 the vessels are undistinguishable from 

 the surrounding cells. Externally to the zone In! we have in fig. 47 the fusiform 

 cells of the prosenchymatous layer of the bark, e, through which the rootlet cushion 

 passes radially. In all my sections an extension of the outer layer, li, of the 



