ta0: BOTANICAL GAZETTE (FEBRUARY 
obovate, narrowly winged, having a broad and shallow emargination ‘ 
‘summit without cusps; rays not seen. 7 
Collected on Chickamauga battlefield, Georgia, October 6, 1898. 
The affinity of this plant is with S. terebinthinaceum, from whith, 
however, it is very different. It is evidently more nearly allied t0 
Elliott’s S. pénnatifidum, which I have not seen, but it does not ag 
with his description — Wn. M. Cansy, Wilmington, Del. 
Bren LETTERS: 
IMPERFECTIONS OF LABORATORY MATERIAL 
THE experimenter must be keenly alive to possible imperfections of - 
material of which his apparatus is constructed, a fact made apparent 
‘recent experience in this laboratory with a bleeding-pressure demons 
The demonstration consisted of a T-tube filled with water, attached 
stump of a plant, and to the short arm an open manometer, filled wi 
‘cury. The pressure of the exuding sap set up a difference of level bet 
the columns of mercury in the arms of about 8™. After this point had: 
reached the mercury remained stationary and the sap appeared to be pas 
‘the mercury in some manner, as it appeared in an increasing amount 0” 
of the mercury in the free arm of the manometer, finally filling ta 
flowing at a height of 60°. This puzzling action was explained by th 
that the manometer tube showed a minute groove throughout its entire 
‘on the inner side of the wall so small that it could not be entered or 
the mercury. This permitted a constant stream of water to pass by a 
other arm of the manometer. Of the many things which may occur 
concert the beginner in studying root-pressure, the above is doubtless 0% 
the most unusual.—D. T. MacDoueat, University of Minnesota. 
