of Goal-Measure Plants. 



165 



section I. 3 shows the phyllotaxis very clearly, also the section 

 reproduced in fig. 7, PI. vi. 



The explanation of the different appearance presented by the 

 several leaf-traces seen in the same transverse section of the 

 stem is afforded by longitudinal sections. In fig. 1, PI. v., the 

 leaf-trace It 1 appears at the top of the section as a dark compact 

 strand clearly differentiated from the more central metaxylem ; in 

 this position it appears as the elliptical group It of fig. 5, PI. v., 

 and It 1, figs. 2 and 7. Text-figure 2 (It) shows the appearance of 

 such a compact leaf-trace as that of fig. 5, PI. v., in longitudinal 

 view. The strand It of fig. 1, PL v., when followed in its downward 

 course is seen to widen laterally, and in the position indicated in 

 the figure by the letters It 1 it is scarcely distinguishable as a 

 distinct strand. This gradual dying-out of the leaf-trace as shown 

 in fig. 1, PI. v., is the expression of the fact that the tracheids 

 gradually spread out in a slightly fan-shaped manner as the trace 

 passes downwards and the long and comparatively narrow tracheal 

 elements become shorter and broader, and finally join on to the 

 large and flat tracheids of the metaxylem. 



m 



Figure 3. Longitudinal Section through Part op a Leaf-trace (It) and the 

 outer portion of the Metaxylem (in). (Section I. 9, x 50.) 



The looser and less clearly limited appearance of the leaf-trace 

 seen in figs. 3 and 6, PI. v., shows that the transverse sections 



