18 



FAMILIES OF FLOWERING PLANTS. 



neys. The pollen, which is produced in great (juanlities during the 

 flowering season, is sometimes employed in })lacc of lycopodium spores 

 as an absorlient powder. 



Family Sparganiaceae. — Bur-reed Family. This also consists of 

 a single genus, Sjxr/r/rnifVf/i, 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. Spargdiiiinn contains about 

 8 species, natives of temperate regions: they are not known to pos- 

 sess any economic uses. 



ORDEK HELOBIAE. 



Family Naiadaceae. — Pondweed Family. About It) 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 

 Ijc noticed in many such situa- 

 tions. All the })ond weeds are im- 

 mersed a<]uatics Avith slender, 

 often branching stems and small 

 greenish flowers usually borne in 

 spikes; they are either perfect 

 (having the stamens and pistils in 

 the same flower), monoecious or 

 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- 



FiG. 14.— ClaspinK-leaved pondweed (Pota- 

 mogeton perfoliatii.'^) with enlargi d fruit and 

 section of the latter. (After Britten und 

 BrowB, 111. Fl. North. U. S.J 



