EQUISETUM. 
249 
when in a luxuariant condition of growth. They grow 
erect, and are from six to seven feet or more in height, 
clothed nearly to the bottom with spreading proximate 
whorls, those on the stouter parts consisting of thirty to 
forty branches, which are sometimes again branched. The 
upper whorls have a less number of branches. The whorls are 
most crowded towards the top of the stem, and there also 
the branches are about the full length— six or eight inches ; 
lower down the stem the branches become shorter, and 
the whorls more distant. The stems measure about 
an inch and a half in diameter at the stoutest part, and 
from this point decrease upwards, becoming very slender at 
the point. The surface is smooth, with mere indications 
of about thirty faint lines extending into the sheaths, and 
there becoming more apparent. The sheaths set close to 
the stem, or nearly so, and are half an inch long, green 
below, with a dark brown ring at top, and divided at the 
margin into slender bristly teeth, about half an inch long, 
dark brown, with paler membranous edges ; the teeth fre- 
quently adhere together in twos and threes. The branches 
have eight or ten ribs united in pairs, and their sheaths 
terminate in four or five teeth, each extended into a slen- 
der black bristle, and having two denticulated ribs. The 
