18 FAMILIES OF FLOWERING PLANTS. 
neys. The pollen, which is produced in great quantities during the 
flowering season, is sometimes employed in place of lycopodium spores 
as an absorbent powder. 
Family Sparganiaceae.—Bur-reed Family. This also consists of 
a single genus, Sparganium, and it was formerly included among the 
cat-tails. The plants possess an entirely different aspect,. however; 
the flowers are monoecious, as in Typha, but they are borne in several 
globular heads on the upper branches of the stem, and not in a single 
terminal spike. (See Fig. 13.) The fruit is hard and nutlike, much 
larger than that of the cat-tail, and without any intermixed bristles, 
while the leaves are thin and grasslike. Sparganinm contains about 
8 species, natives of temperate regions; they are not known to pos- 
sess any economic uses, 
ORDER HELOBIAE. 
Family Naiadaceae.—Pondweed Family. About 10 genera, widely 
distributed, of which Potamogeton is the only one of much size or 
importance, containing about 50 
species, 30 of which occur in the 
eastern United States and a large 
proportion of them in New Eng- 
land alone. Slow streams and 
rather shallow ponds form the 
favorite haunts of these plants, 
whose smooth oval leaves floating 
on the surface of the water may 
be noticed in many such situa- 
tions. All the pondweeds are im- 
mersed aquatics with slender, 
often branching stems and small 
greenish flowers usually borne in 
spikes; they are either perfect’ 
Fig. 14.—Clasping-leaved pondweed (Pota- (having the stamens and pistils in 
mogeton perfoliatus) with enlarged fruit and : F = . : 
section of the latter. (After Britton and the Same flower), monoecious oF 
Brown, Ill. Fl. North. U. 8.) dioecious, in some cases wholly des- 
titute of floral envelopes, in others 
with a perianth of four distinct segments. In this latter respect it 
will be seen that they are exceptional among the monocotyledons, 
which it will be remembered are usually distinguished by the three- 
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