576 POLYGONUM. [CLASS VJII. order II. 



with its sleader steins and copious leaves, but its herbage is eaten with 

 a relish by all cattle, and its abundant seeds abounding in nutri- 

 ment, afford a large supply of food to small birds. And according to 

 Thunberg, a dye is prepared, from the plant resembling in colour the 

 indigo, a property which might be found of very considerable value in 

 our own country. 



10. P. du'bium, (Fig. 656.) Dubious Knot-grass. Flowers axillary • 

 leaves'glaucous, elliptic-lanceolate, rough on the margins, flat ; stipules 

 very short, six ribbed, bifid, shortly much divided ; stem herbaceous, 

 rigid, wiry, much branched ; fruit longer than the perianth, smooth 

 and shining ; root annual. 



Root stout, long, twisted, fibrous, somewhat woody, branched. 

 Stems several from the same root, glaucous, angular, and strongly 

 striated, the joints numerous, from one and half to two inches apart, 

 leafy and branched, prostrate and spreading, hard and wiry. Leaves 

 alternate, elliptic-lanceolate, flat, with a rough somewhat crenated 

 margin, tapering at the base into a short footstalk, obtuse or acute at 

 the point, the mid-rib and lateral veins slender. Stipules at the base 

 of the leaves at first tubular, and cleft into two lanceolate segments, 

 greenish brown]^at the base, the margin pale, thin, membranous, very 

 shortly much torn into narrow spreading segments, the base with six 

 prominent stout ribs, rarely any slender intermediate ones. Inflo- 

 rescence axillary clusters, of from one to three flowers, sessile, and 

 elevated on short slender simple stalks. Perianth of four or five oblong 

 acute segments, divided nearly to the base, each with an acute mid- 

 rib, green at the base, the margin while or pink. Stamens scarcely 

 half as long as the perianth, the filaments dilated at the base into an 

 ovate form, above awl-shaped. Anthers small, ovate, yellow. Styles 

 very short, the stigmas small, obtuse. Fruit about half as long again 

 as the perianth, ovate, acute, pointed with the base of the styles, acutely 

 triangular, quite smooth and shining, of a chesnut brown colour, loosely 

 enveloped in the persistent perianth. 



Habitat. — Waste places near the sea ; Looe Bar, Cornwall. 



Annual ; flowering during the summer months. 



The only specimens we have of this plant are from the station above 

 given ; its habit is that of P. aviculare, but its stems are hard, wiry, 

 rigid, and rough, with the elevated stria. The stipules are shorter, and 

 torn into numerous narrow segments almost before the flowers are 

 expanded ; the filaments are dilated into a broad ovate form at the base, 

 in which characters it difi'ers from P. aviculare, but more especially in 

 the size, form, colom*, and surface of the nuts, which are only loosely 

 enveloped, not closely invested with the persistent perianth, as that of 

 P. aviculare. The similarity|]of the nuts to the following species seems 

 to connect them with it, while the flat leaves and six ribbed stipules 



