248 STUDIES IN FOSSIL BOTANY 



answer to them morphologically. A characteristic 

 feature of the Stigmarian bark is the great tangential 

 dilatation of the more external peridermal cells. 



The above must suffice for a general account of the 

 anatomy of the Stigmarian axis ; it remains to describe 

 its appendages, and their relation to the parent organ. 



As already mentioned, the appendages, which we 

 will call simply rootlets, following Williamson's termin- 

 ology, are arranged in quincuncial order on all parts of 

 the Stigmarian surface (see Fig. 97). The vascular 

 strand of each rootlet, so far as its xylem is concerned, 

 starts from the inner, primary margin of the wood of 

 the main axis, and bends sharply outwards, taking a 

 nearly horizontal course through the secondary xylem. 

 Every principal ray is traversed by one of these 

 rootlet-bundles, which appear in tangential sections of 

 the axis as tongue-shaped bodies, with the point pro- 

 jecting freely into the lenticular cavity, left by the decay 

 of the ray, while the base is continuous with the 

 adjacent wood (see Fig. 99). The orientation is such 

 that the free point (protoxylem) of the rootlet-strand is 

 directed towards the apex, while its connection with the 

 wood is towards the base of the main axis. 1 Thus the 

 water absorbed by the rootlet would have been directly 

 conducted through the wood of the main organ, to the 

 aerial stem. 



The xylem- of the rootlet was increased to some 

 extent with the growth of that of the main axis, for the 

 strand becomes larger as we follow it outwards through 



1 Thus in Fig. 99 the growing point of the Stigmaria would have lain 

 in the downward, and its base in the upward direction, as the figure is 

 drawn. 



