32 BOTANICAL GAZETTE [JANUARY 
leptome side, besides one (jig. 5, S), or sometimes two or three 
cells on the hadrome side, between the large vessels. Selecting 
one of the largest bundles in the leaf, the sheath appears as a 
closed continuous sheath (fig. 4, S) all around the leptome and 
hadrome. It seems characteristic of this inner sheath to show 
interruptions in the small mestome bundles, and to become con- 
fined in the leptome alone in the smaller of them. I regret that 
I was unable to decide whether the inner sheath is also devel- 
oped in the smallest of the mestome bundles, the anastomoses. 
The tissues are so little differentiated in these that it seemed 
impossible to decide whether the sheath was present or not; the 
outer one, however, was plainly visible. So far there would be 
no valid objection to considering the inner sheath as identical 
with a mestome sheath,® which, in several Graminez, exhibits 
the same kind of interruptions in the various forms of mestome 
bundles. However, there are two reasons for feeling uncertain 
about its identity. It is absent in the mestome bundles of the 
scape, where two or three strata of stereomatic tissue have taken 
its place within a true endodermis, and in longitudinal section 
the cells differ in a marked degree from those of a mestome 
sheath, being very long, with almost horizontal cross walls. 
Moreover, the thickening of the inner cell wall does not show 
the same structure as in typical mestome sheaths, where this 
wall almost constantly exhibits a conspicuous thickening in con- 
trast to the outer wall. When treated with concentrated sulfuric 
acid, however, the sheath in Eriocaulon showed the same resis- 
tance as in the endodermal sheaths in the mestome bundles in 
the cortex of the rhizome. If the outer sheath represents a 
parenchyma sheath, one might feel justified in considering the 
inner as a somewhat modified mestome sheath; but since it does 
not seem possible to separate the outer sheath from the collen- 
chyma, I can at present suggest no other term for the inner one 
than simply a protective sheath. 
Poulsen attributes two sheaths to the mestome bundles in the 
® SCHWENDENER, S.: Die Mestomscheiden der Gramineenblitter. Sitzungsber. 
K. Acad. Berlin 405. 1890. 


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