24G LYCOPODIALES [CH. 



Lepidodendron fuliginosum, the rootlet bundle is accompanied 

 by a parichnos strand, but this has not been detected in the 

 ordinary Stigmaria ficoides. When free from the parent axis a 

 rootlet usually consists of an outer cylinder of cortex enclosing 

 a broad space in which remnants of lacunar tissue are some- 

 times seen. The relation of the external features of a well- 

 preserved Stigmarian rootlet-scar to the internal structure of a 

 petrified rootlet is very clearly seen on comparing such sections 

 as those represented in fig. 210, D, with the form of the scar on 

 a Stigmarian cast. A specimen figured by Hooker^ in 1848 

 affords a good illustration of the structure of a rootlet-base as 

 seen in an unusually complete cast; this correlation of ana- 

 tomical and surface features is clearly described also by 

 Williamson^ and by Solms-Laubach^. It is probable that 

 even during life the rootlets were hollow for a part at least 

 of their length as are the roots of Isoetes (fig. 133, G). 



An interesting discovery was made a few years ago which 

 confirmed a statement by Renault which Williamson was 

 unable to accept, namely that the xylem bundle of a rootlet 

 occasionally gives off a delicate tracheal strand at right angles 

 to the long axis of a rootlet. In some rootlets Weiss* found 

 obliquely running delicate strands of xylem, surrounded by a 

 layer of parenchymatous tissue, in the space between the 

 vascular bundle and the outer cortical cylinder. It is clear 

 that a few spiral tracheids are occasionally given off from the 

 protoxylem of a rootlet bundle : these follow an oblique course 

 to the outer cortex, where in some cases they have been traced 

 into connexion with short and spirally marked cells resembling 

 transfusion tracheae (fig. 210, A). This arrangement may serve 

 as a means of facilitating the passage of water absorbed by the 

 superficial cells into the xylem strand. It should be noticed 

 that, like roots of recent water-plants, the rootlets of Stigmaria 

 had no root-hairs. Fig. 210, F, shows a transverse section of 

 part of a rootlet in which the outer cortical cylinder, c^ is 

 connected, as in the roots of Isoetes, with the sheath siirround- 



1 Hooker (48^) Pis. i. ii. The sections of Stigmaria figured by Hooker are 

 in the British Museum (V. 87541 

 2 Williamson (87) A. PI. xii. » Solms-Laubach (91) A. * Weiss, P. E. (02). 



