Sod (Sg. Sada ha ra 
; a, ea cs 5 
LEITNERIA FLORIDANA. VAS) 
a few tracheides and spiral vessels about 20 » in diameter, 
surrounded by wood parenchyma. Aside from this, except 
where the bundles pass out to the leaves, no true spirals 
occur in the stem. The remainder of the xylem consists 
of pitted tracheides and ducts, wood parenchyma, and, 
chiefly, libriform cells. Except for the spiral vessels men- 
tioned above, the vascular elements of the wood are all 
furnished with bordered pits, a scalariform reticulation 
marking their contact with the medullary rays. 
The pitted vessels are distributed through the stem in a 
characteristic way, as is usual in woody plants. Each year’s 
growth in the secondary wood begins with a greatly inter- 
rupted row of vessels large for the plant, and measuring 
from 50 to 95 » in diameter. In addition to these vernal 
ducts, each year’s zone of wood contains a number of 
groups of similar but smaller vessels, which are arranged 
either approximately parallel to the circumference or with 
an oblique direction outwards, often strongly accentuated 
in the older wood where it may become quite radial, and, 
as acommon thing, grading in size from the middle to each 
extremity or from one end to the other, most diameter 
measurements lying between 25 and 35». These groups 
consist of the elements usual in such duct accumulations, 
namely vessels, tracheides, and wood parenchyma. The 
vessels show a complete disappearance of the cross septa 
which originally divided the vertical rows of rather short 
cells from which they arise, except for a narrow ring 
around the margin, in this respect differing very markedly 
from the similar vessels of Liriodendron, Liquidambar, 
etc., where the perforations are formed in such a way as to 
leave the original septum as a persistent scalariform plate 
running obliquely across the mature duct. 
The wood parenchyma, which is not abundant, and stands 
in close connection with the ducts and annual rings, does not 
differ particularly from the parenchyma already described 
about the secretion passages in the pith sheath. The tra- 
cheides as arule are similar to the libriform or common wood 
15 
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