CAEBONIFEEOUS LYCOPODS AND SPHENOPHTLLS. 71 



of those figured by Prof. Williamson, whose example seems to 

 have been much encrusted (No. 815). 



"We are therefore dependent on amorphous casts, some of which 

 show more or less plainly the course of the rootlet bundles from 

 the xylem cylinder to the rootlets. One such specimen is figured 

 by Williamson, '^ two are given by Goppert, " and another by 

 Zeiller.^ Solms-Laubach also describes a specimen which shows 

 the course of the rootlet bundles. * 



A specimen in my collection (No. 981) also shows the course of 

 the rootlet bundles. The fossil is preserved in fine-grained sand- 

 stone and has been split through the axis. The position of the 

 vascular cylinder is indicated by a depression up the centre of the 

 fossil, from which narrow channels run outwards and upwards. 

 Occasionally associated with these are small cord-like casts, 

 smaller than the channels through which they pass, and which 

 are the bundles or bundle with bundle-sheath. The outer surface 

 of the specimen exhibits the characteristic scars. 



The rootlets are attached to a specialized structure in the outer 

 bark, which Prof. Williamson has designated the rootlet-cushion. ^ 

 This consists of a cylindrical mass of very dense cells embedded 

 in the parenchyma of the bark, and ending in a conical point 

 within the base of the rootlet. The outer surface of this cushion 

 bears a layer of elongated branching tubular cells, whose special 

 function is not yet ascertained. In impressions of Stigmaria the 

 small area enclosed within the circle which contains the small 

 central vascular cicatrice is the peripheral limit of the rootlet- 

 cushion. Prof. Williamson was of opinion that there was " no 

 kind of ' articulation ' where the root was planted upon the bark," 

 and that the separation of the rootlet was either the result of 

 external force or decay "producing a variable contour in what 

 remained of the torn tissue of the rootlet." " 



^ Williamson, Monog. Stigmaria, p. 24, PI. XII., fig. 37. 



- Goppert, Gatt. der Fots. Pflanztn, Lief. I. -II., PI. X., fig. 17 ; PI. XI., 

 fig. 18. 



' Zeiller, Flore foss. Bassin houil d. Valtndtnnes, p. 617, fig. 45, Text, 

 1888. 



* Solms-Laubach, Fossil Botany, p. 274. 



^ Williamson, Monog. Stigmaria, p. 26. 



•= Williamson, ibid., p. 38. 



