1901] ERIOCAULON DECANGULARE 31 

in regard to it in the leaf, where there is to be observed 
collenchyma and another form of tissue which superficially 
resembles stereome, but which shows such strange occurrence 
and development that it is not even to be considered as a modi- 
fication of this tissue. The collenchyma in the leaf is thinner 
walled than in the stem, and accompanies the mestome bundles 
mostly as hypodermal groups on both faces. It appears to be 
more strongly developed on the lower face than on the upper, 
but each group is composed of only three or four layers of these 
cells (fig. g, M). Around each mestome bundle is a sheath, 
which at first glance was considered identical with the paren- 
chyma sheath (fig. 5, M), as seen in many genera of other 
orders. A longitudinal section, however, showed a structure 
very unlike that of a typical parenchyma sheath. The cells 
were relatively very long, and I was unable to separate them 
from the adjoining cells of the collenchyma, inasmuch as they 
both showed the same rapid dissolution when treated with con- 
centrated sulfuric acid. It is somewhat strange, also, that no 
trace of this outer sheath was found in the stem, a fact which 
seems to be in favor of the supposition that it is not identical 
with a true parenchyma sheath. When such sheaths are devel- 
oped, they seem to follow the mestome bundles not only in the 
leaves but also in the stem, at least in those which are in the 
cortex, but not in the pith. 
An examination of one of the large mestome bundles ( fig. 
4) reveals the fact that still another sheath (.S) occurs within 
the first. This is distinctly thicker walled than the outer, the 
cells are very much smaller, and the walls are very bright 
-yellow in contrast with the surrounding collenchyma. In longi- 
tudinal section the cells of this inner sheath are quite long, 
with mostly horizontal cross walls. A study of its occurrence 
throughout the leaf has assured me that it does not show the 
Same development in all the mestome bundles. In smaller 
bundles the sheath is a mere arch on the leptome side, while the 
vessels border immediately on the outer collenchymatic sheath. 
In the larger mestome bundles there is the same arch on the 
