august] BOTANICAL GAZETTE 



114 



bands of parenchyma, arc usually well rilled with starch and occa- 

 sional calcium oxalate crystals. 



Medullary rays.— The medullary rays are of three types, 

 namely, narrow uniseriate rays, a single layer of cells wide and 

 several cells deep; multiseriate rays, two to several cells in width 

 at their widest point and of variable longitudinal extent; and 

 broad foliar rays or leaf gaps, which in tangential view resemble 

 the aggregate ray of Quercus. The last are distributed at fairly 

 equal intervals throughout the woody cylinder and always extend 

 from the pith to the cortex. They are further characterized by 

 the presence of at least one mucilage duct and one leaf trace 

 bundle situated in the lower central part of the gap (rig. 6). A few 

 isolated cases occur where two ducts and even two traces may be 

 seen in a single foliar ray. 



Course and structure of leaf trace in gap 



The course of the leaf trace through the parenchymatous gaps 

 or foliar rays from pith to phloem is approximately level, except 

 for a slight downward curve of the strands due to their manner of 

 formation. The bundle is endarch throughout its course in the 

 gap and through the phloem, the xylem of the bundle usually 

 uppermost and just beneath the duct, with no change in orientation 

 until the bundle reaches the cortex, where it is continuous with one 

 of the oblique cortical strands. 



The manner of connection of this foliar trace with the primary 

 and secondary wood of the main stele is one of the most striking 

 and interesting features of the wood. Within a short distance 

 of the pith the strands of the trace curve downward, the primary and 

 secondary elements uniting with like elements of the main cylinder. 

 On the interior vertical face of the wood at the point of union, and 

 continuing up through the gap, always on the upper side of the 

 trace (figs. 3-5) where the primary vessels of the trace would 

 naturally appear, are peculiar tracheidal elements, curiously 

 reticulated, in some cases forming continuous vessels, in other 

 cases merely isolated patches of lignified tissue. These irregular 

 fibrous elements are best illustrated in fig. 2, where a longitudinal 

 section of the upper portion of the trace appears in a transverse 

 section of the wood. 



