of Goal-Measure Plants. 145 



leaf-trace (PL III. fig. 3, It 1). In the left-hand portion of fig. 3, 

 PI. in. the leaf-trace It 1 is seen to have considerably encroached on 

 the secretory zone s, s, so that the large clear sacs of the latter 

 tissue extend as an arched row external to the outlying trace ; the 

 other leaf-trace, It 2, has advanced rather further, and here the 

 continuity of the secretory zone is interrupted. As the leaf-trace 

 pursues its course, the tracheal strand is accompanied by a group of 

 elements from the secretory zone; this group is shown in fig. 3 

 as a dark and ill-defined patch of tissue immediately in front of the 

 leaf-trace It 2. Each leaf-trace also carries with it a small strand of 

 parenchyma from the meristematic zone a (fig. 3, etc.). These facts 

 may be more precisely expressed by the statement that a leaf-trace, 

 as it appears in the cortex of a stem, consists of a group of tracheids, 

 a group of secretory elements, and a few intervening layers of cells 

 which are continuous, as demonstrated by longitudinal sections, 

 with the xylem of the corona, the secretory zone s, s, and the 

 meristematic zone a respectively. The detailed structure of the 

 leaf-trace and the accompanying tissues is more clearly shown in 

 sections 2 and 3. 



<y Cortex. 



Beyond the secretory zone (s fig. 3, etc.) there is a fairly definite 

 layer of tangentially elongated cells (the uppermost layer in fig. 12, 

 PI. IV.) suggestive of an endodermal layer. Beyond this there are 

 several layers of compact parenchyma constituting a band of 

 tissue about equal in breadth to the secretory and meristematic 

 zones together ; the innermost part of this region is shown at the 

 edge of fig. 3, PL III. This band passes outwards into a tissue 

 composed of more radially elongated elements of the nature of 

 fairly closely packed trabeculae, agreeing exactly with the rather 

 loose tissue described by Bower 1 in Lepidostrobus Brownii and by 

 other writers in Lepidodendroid stems. This hypha-like or trabe- 

 cular middle cortex occupies the greater portion of the stem ; 

 towards the periphery of the section it is succeeded somewhat 

 abruptly by 1 — 2 layers of more regularly arranged tangentially 

 elongated elements separated by conspicuous intercellular spaces, 

 and beyond them by a compact parenchyma, of which the cells 

 become thicker walled towards the limits of the section where 

 they constitute the outermost tissue ; this more compact paren- 

 chyma is spoken of as the outer cortex. 



The less perfect stele seen in Section 1 agrees in size and 

 structure with that shown in Text-figure 1, but there is one 

 feature of interest not represented in the more perfect stele. 

 Some of the parenchymatous elements between the secretory zone 



1 Bower (93), PI. xvn. fig. 13. 



