458 THE GENUS ISOETES IN NORTH AMERICA. 
covered with water, and fully exposed to the hot sunshine of that season. Three weeks [371 (14) ] 
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, 4 to 14 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, bearing 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 diam- 
eter, with both ends strongly elevated, their edges already showing small masses of black decayed 
tissue (the remnants 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 Jsoétes, 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 varie- 
ties, 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 rier water ; 
a few are always submerged and are found out of water only in abnormal conditio 
e. g. in unusually dry seasons. The majority are of amphibious growth, entirely or a [3872 (15) ] 
tially submerged during the wet seasons, in winter and especially in early spring; but 
at the growing season they partially get out of the water, leaving only their trunk and lower part of 
the leaves immersed. These species do not come to perfection when completely immersed, though 
they may not be entirely infertile; it seems that partial exposure to the atmosphere is necessary to 
their well-being. A variety of the amphibious species are the tidal ones, which are alternately 
emerged and submerged during the changes of the tides; they are found in the estuaries of some of 
our Atlantic rivers. Then we have a few species which we are justified in calling terrestrial, as we 
find them, when fully developed, on dry land; but it seems that for their germination and their 
growth in early spring they also require moisture and water; we therefore find them on low or flat 
grounds which may be overflowed in spring, or in springy localities, but they fully develop and 
become fertile only when out of water. J. melanopoda, which belongs to this class, normally ma- 
tures in June or early in July, and its leaves wither before the end of that month; by keeping 
it immersed, however, I have kept it fresh and growing throughout the summer, but under these 
conditions it remained perfectly sterile. Those terrestrial species which grow on arid hills around 
the Mediterranean must require even less moisture, and are probably satisfied with temporary 
drenchings. 
The submerged and the amphibious species are generally found, some in soft mud, others be- 
tween gravel and stones; the amphibious ones generally in deep mud. Our terrestrial species grow 
mostly in heavy, retentive soil. 
