150 Mr Seward, Notes on the Binney Collection 



as represented in PI. IV. fig. 10; the irregularly shaped and 

 more faintly drawn cells on the inner side of fig. 10 are the most 

 external elements of the middle cortex ; these are succeeded by 

 rather darker and much more regularly disposed cells separated 

 from one another by intercellular spaces, and beyond this we pass 

 into the more compact outer cortex. Section 3 illustrates excep- 

 tionally well the structure of the leaf-traces (PL III. figs. 1 and 2 ; 

 PI. iv. fig. 7). In fig. 7, PL iv., the xylem strand of a leaf-trace 

 is represented as it appears close to the point at which a trace 

 becomes detached from the corona ; the protoxylem elements, px, 

 are clearly internal, thus giving to the foliar bundle a mesarch 

 structure. 



Figure 1, PL ill. 1 , represents a leaf-trace in slightly oblique 

 transverse section in the middle cortical region of Section 3 as 

 it ascends steeply or almost vertically towards the surface of the 

 stem. The group of tracheids has altered its shape as compared 

 with that shown in fig. 7, PL iv.; in the more flattened leaf- 

 traces the protoxylem is not so clearly indicated, but it may 

 sometimes be detected as a short crushed band in the interior 

 of the tracheal strand. Between the xylem and the group of dark 

 elements s (fig. 1, PL in.) there are 3 — 4 rows of slightly elongated 

 parenchymatous cells, which agree with the tissue of the meri- 

 stematic zone of the stele with which they are in continuity. The 

 group s consists of polygonal elements varying in size and associated 

 with patches of a dark brown substance, probably a product of 

 secretion. In longitudinal sections of leaf-traces the elements of 

 this group s are seen to be, in part, long cells with square ends and 

 often partially filled with a dark brown secretion (PL iv. fig. 11). 

 This tissue is usually imperfectly preserved, and the elements 

 composing it often appear in a more or less disorganised 

 condition. 



The leaf-trace is surrounded by a few layers of parenchy- 

 matous cells, which may be spoken of as constituting a peridesm 2 . 

 In fig. 2, PL ill. a leaf-trace is shown in the outer cortical region of 

 the stem : the secretory strand s is less perfectly preserved than 

 in fig. 1 ; but the chief difference is the presence of a well-marked 

 crescent-shaped group of tissue which partially encloses the leaf- 

 trace externally; this consists of the parichnos, a mass of the 

 middle cortex which passes out with the leaf-trace in its course 

 through the outer cortical zone. The looser and more irregular 

 structure of the parichnos, p, is in marked contrast to the more 

 compact tissue of the outer cortex as shown at the edge of 

 fig. 2, c. 



1 Cf. Bertrand (91), PI. vm. fig. 80. 



2 van Tiegkem (90), p. 434. 



