4 Weiss, Root-apex a7id Young Root of Lyginodendro7i. 



Some justification is perhaps needed for assigning 

 this and similar root-tips to Lyginodendron. Their fairly- 

 constant association with undoubted older roots of 

 Lygmodendron would in itself be insufficient evidence, 

 were it not strengthened by a very large series of rootlets 

 showing every stage of transition, from root-tips in which 

 no vascular tissue is as yet to be seen, to fully mature 

 rootlets showing the typical structure of Lyginodendron. 

 In addition, we find in all the rootlets evidence of the 

 differentiation of the more external into an outer large- 

 celled tissue and an inner small-celled coitex, the latter 

 possessing numerous secretory sacs with dark contents. 

 The presence and position of these latter cells renders 

 the identification of the rootlets a fairly easy matter. 



The first examination of the root-apex shown in 

 Fig. I, particularly as on focussing somewhat deeply a line 

 marking the limit of the plerom cylinder becomes 

 visible, led me to infer that the roots did not possess a 

 single apical cell ; but a closer examination has caused 

 me to believe that the section is not sufficiently median to 

 enable this conclusion to be drawn from it. In the upper 

 part of the rootlet, which, as can be seen from the smaller 

 diameter, is cut tangentially, a secretory sac is shown 

 in the middle portion of the section, which indicates that 

 the section here shows only cortical tissues and not those 

 of the central cylinder. Nearer the apex, though the 

 limits of the central cjdinder can be made out by focus- 

 sing more deeply, the same still holds good, and the small 

 dark cell near the centre of the section is still one of 

 the secretory cells of the cortex and not part of the 

 central cylinder. It follows, therefore, that the evidence 

 of this somewhat tangctical section will not warrant the 

 conclusion that the root did not possess a single apical 

 cell. 



