4 BUTTERWORTH, Structure of Psaronius. 



The inner thin-walled cortex is in some roots very well 

 preserved, in others it is entirely disorganised. The thick- 

 walled outer cortex is of course very well preserved, and 

 seems slightly thicker in extent than the same layer in 

 Psaronius reiiaultii. On the outside of this outer cortex 

 numerous multicellular hairs are given off, which form a 

 complex, felted mass of elongated cells between the 

 adjoining roots. 



The presence of secondary thickening is distinctive 

 ■ in my new Psaronius. It occurs to a varying extent 

 in different roots of my specimen. Sometimes the 

 secondary increase takes place only on one side of 

 the central cylinder, as in Fig. i, {c)\ sometimes the 

 roots increase uniformly in thickness on all sides of the 

 central cylinder, as in Fig. 2. In all cases of secondary 

 thickening the primary groups of wood become separated 

 by the formation of secondary wood between the primary 

 rays. This is well seen by comparing, in Fig. i, {c), the 

 primary rays without secondary thickening with those rays 

 in connection with which secondary wood has been formed. 

 It is clearly seen, in Fig. 2, that this interstitial secondary 

 wood has forced the xylem rays apart. This first-formed 

 portion of the secondary wood is composed of cells which 

 are not so regularly arranged as the later secondary 

 wood beyond the protoxylem groups, which forms, as 

 seen in Fig. 2, a continuous cylinder. Here the cells are 

 arranged in rows and present a very typical appearance of 

 cells formed from a secondary meristem. These cells of 

 the secondary wood, where they are cut slightly obliquely, 

 show a scalariform marking similar to that of the primary 

 vessels. Medullary rays, if present, do not show distinctly 

 in the transverse section, and those roots which showed 

 secondary wood were not long enough for longitudinal 

 sections to be cut from them. The secondary phloem too, 



