CARBONIFEROUS LYCOPODS AND SPHENOPHYLLS. 69 



of three feet. 1 This is a greater length than that usually 

 ascribed to them, but it is extremely rarely that their full length 

 can be seen. They bifurcate, but specimens showing this 

 character are not very common. Such bifurcations are figured 

 by Artis, 2 Corda, 3 and Goldenberg. 4 In the example given by 

 Corda the rootlet, including the bifurcation, is about nine inches 

 long. The extremity of a dichotomous rootlet is also figured by 

 Williamson. 5 At the point from which the arms of the dicho- 

 tomy spring there is a slight contraction, but specimens of 

 dichotomizing rootlets which retain their structure do not show 

 any indication of this constriction. ,; It may be due to a contrac- 

 tion of the tissues through shrinkage. 



The outer layer of the rootlet is formed of thick-walled 

 parenchyma, which is an extension of the outer cortical layer of 

 the rhizome. The space within this outer wall is almost invari- 

 ably devoid of all structure, the delicate tissue which once 

 surrounded the bundle-cylinder having disappeared, if such ever 

 existed. Prof. Williamson thinks it is probable that the rootlets 

 were fistular as in Isoetes lacustris, except at the extreme base of 

 the rootlet where it was embedded in the outer parenchyma of 

 the bark. 7 



I have, however, detected slight remains of a cellular tissue 

 which may have filled this part of the rootlet, but not knowing 

 the exact position of my section, it may be from the basal region 

 of the rootlet, where we know a parenchymatous tissue existed. 



Within the outer envelope described above, is the bundle- 

 cylinder, composed of a few roses of very delicate cells, and con- 

 taining the vascular bundle. At first the rootlet bundle consists 

 of a single small scalariform tracheid, but to this others are 

 subsequently added. In form the bundle is oval or deltoid, with 



1 London, Edin., and Dublin Phil. Mag., 3rd Ser., Oct., 1845, p. 243. 



" Artis, AjUedil. Phyt., PI. III. 



s Flora d. Vorwelt, p. 32, PL XII., fig. 1. 



4 Goldenberg, Flora Sarcep. foss., Heft. III., p. 17, PI. XIII., fig. 1. 

 Ibid., p. 19, PI. XIII. , fig. 5 (under name of Stigmaria anabathra). 



5 "Monog. Stigmaria ficoides," p. 32, PI. XIII., fig. 27. (Palceont. Soc., 



1887.) 



c Williamson, Monog. Stigmaria ficoides, p. 33. PI, XI., fig. 63. 

 7 Monog. Stigmaria, p. 25, 



