14 ENGELMANN-THE GENUS ISOETES IN N. AMERICA. [ 37 1 
fully exposed to the hot sunshine, of that season. Three weeks 
later the first green points were seen and continued to come up 
until the end of October, while at that time the earlier ones had 
already developed 5 to 8 leaves, £ to 1 1 inches in length. The 
contents of the large or female spore-cell first developed into a 
dense cellular mass; this, enlarging, split the cell-coats as above 
described and protruded obliquely upwards a minute conical 
point, green inside, while on the lower edge of the opening, but 
still between the three valves (the lower hemisphere of the spore- 
case not being ruptured or perforated at all), a much smaller and 
rounded knob, the origin of the first rootlet, showed itself, bear¬ 
ing a large number of extremely fine capillary fibres ; the bulk of 
the prothallus remained enclosed in the hemispherical part of the 
spore-case as a lateral knob, while the first leaf and then the first 
rootlet elongated ; the spore-case was thrown off only when the 
former had acquired a length of 3 to 4 and the latter one of 2 to 
3 lines, the capillary fibres still continuing at the origin of the 
rootlet. Soon afterwards a second leaf and a second rootlet were 
formed, both opposite to the laterally protruding spore-mass ; after 
that new leaves and new roots spring up in distichous order 
between the older ones, the youngest in the centre. In twelve 
months the young plant, not yet fertile, shows the bilobed flat 
or rather concave trunk, 2 to 4 lines in diameter, with both ends 
strongly elevated, their edges already showing small masses of 
black decayed tissue (the remhants of the first year’s growth). 
The leaves of these yearling plants, 10 to 15 in number, are 3 to 
4 inches long, have abundant stomata, but as yet only a single 
very slender bast-bundle, median on the upper surface. 
The species of Isoetes , perhaps 40 to 60 in number (according 
to the views taken of the different forms, whether species or 
varieties), are distributed over the whole globe, apparently more 
abundant in the temperate than in the tropical zones. In North 
America we have 13 species, with 12 varieties, to which I add one 
from Cuba ; from Mexico we have received as yet none. More 
are expected to be found when the attention of collectors is more 
earnestly directed to them. 
Most of the species may be called water-plants, growing in 
stagnant or in slow-running water; a few are always submerged 
and are found out of water only in abnormal conditions, e.g. in 
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