of Goal-Measure Plants. 



167 



pitted protoxylem elements, the inner elements having passed over 

 into the large metaxylem tracheids. 



It 



m 



Figure 4. Longitudinal Section showing a few Leaf-trace Tracheids It, 



BETWEEN THE SECONDARY Xi'LEM X 2 AND MeTAXYLEM 111. (Section I. 8, X 16.) 



The structure of a leaf-trace as it passes in an obliquely 

 horizontal direction through the secondary wood is shown in fig. 10, 

 PI. VII. ; in the upper part of the section the secondary tracheids 

 are considerably bent and contorted; in the region a these begin 

 to bend outwards and become continuous with the secondary 

 tracheids of the leaf-trace. The central part of the trace x 1 , has 

 practically the same form as that shown in fig. 5, PI. v., but the 

 primary strand is now enclosed by a zone of secondary wood, 

 the outer elements of which are in continuity with the tracheids 

 of the secondary xylem of the stem. The appearance of a leaf- 

 trace as seen in fig. 10, PL VII., resembles that of a stem of 

 Heterangium, but there are certain differences in detail to which 

 reference is made in the comparison of the Binney specimen with 

 other Palaeozoic genera. Section I. 7 shows the leaf-trace 

 represented in fig. 10, PL VII., and Sections I. 5, I. 6, and I. 8 also 

 illustrate the convolutions of the secondary tracheids of the stem 1 

 in the immediate neighbourhood of the emergent leaf-trace. The 

 transverse Section I. 2 passes through the stem near a leaf-trace, 

 as shown by the oblique position and generally disturbed appear- 

 ance of some of the tracheids and medullary rays. 



1 Cf. Lyginodendron robustum, Seward (97), PI. vi. fig. 11. 



