Pe A oe 
FRESH WATER SKETCHES. 337 
leaves, and be isolated with great ease by the method of macera- 
tion and partial decomposition above mentioned. A better plant 
for exhibiting this peculiar form of vegetable tissue can scarcely 
be found. 
Among the most interesting of the aquatic plants are the Duck- 
weeds (species of Lemna) some of which are the smallest of all 
flowering plants, and yet possess every essential organ. The leaf 
and stem are confounded while the root is reduced to one or more 
capillary fibres, in the centre of which minute spiral vessels may 
be detected. On the surface of the pond, are stomates or breath- 
ing-pores of the usual form, and among its cells may be found 
starch globules and a few cylindrical and stellate groups of crys- 
tals. The flowers are the simplest possible, consisting of two 
staminate and one pistillate flower, supported by a scale-like 
to maturity, and discharges its pollen in advance of the other. 
The pollen, when received upon the stigma, develops pollen-tubes 
as in other plants. In short, no structure or function of the 
larger plants is wanting in these dwarfs of Flora’s kingdom. The 
Duck-weed is one of the plants which often form “‘ the green man- 
tle of the standing pool,” which is often considered as the evi- 
dence of impurity, but which, like all growing vegetation in such 
situations, by absorbing nitrogenized matters and evolving oxygen 
serves to purify and sweeten the water. Any one may convince 
himself of this important agency of growing plants by putting 
a little decaying organic matter in two vessels of water, one of 
which has growing plants immersed in it, and the other has not. 
The last will be putrid and offensive in a few days, while the for- 
mer may be kept for months in a pure condition. The Lemna 
may be easily kept in a glass of water with a little pond mud at 
the bottom, and may be thus watched in all its stages of develop- 
ment. It will be found that it has the singular habit of hiberna- 
ting. On the approach of cold weather, it will be seen to sink to 
the bottom of the vessel where it will remain all winter, but will 
rise again to float on the surface as soon as it feels the warmth of 
the vernal sun. 
Let us now quit the earface of our pond, and, looking below, see 
what we can find in its “green and glassy gulfs.” True to our 
plan of only attending to the microscopic, I shall not stop to de- 
