THE BUCKWHEAT TRIBE. 141 



on which nothing else can grow, equally regardless of 

 hunger and parching thirst. Nay, do not start at 

 this strange description ; it is literally as well as figu- 

 ratively true. 



Knot-grass (Polygonum aviculare, Plate XL. 1.) 

 is one of the commonest of European weeds ; where- 

 ever a seed can take root in the neighbourhood of 

 man, and where nothing else, not even a Stonecrop, 

 can fix itself, there you will find Knot-grass, lying- 

 prostrate on the soil, and continually spreading away 

 from a common centre. Its stems are slender, and 

 wiry ; its leaves are narrow and oblong, with a curious 

 pair of fringed, ribbed stipules at the base (jig. ^2. a.), 

 surrounding the stem, and forming a sort of tube 

 through which its joints pass ; such stipules, which 

 are very uncommon, have obtained the technical name 

 of ochrece or boots. The flowers are sessile and axil- 

 lary in the bosom of the leaves. They consist (Jig. 

 3.) of a calyx divided into five imbricated parts, which 

 unite at the base in an herbaceous tube. Into the 

 throat of the tube are inserted seven stamens (Jig. 4.), 

 of equal length, but having no certain position with 

 respect to the lobes of the calyx ; constituting how- 

 ever, in theory, almost one whorl and a half. The 

 ovary (Jig 5.) is an oblong, three-cornered body, with 

 three separate stigmas, and one erect ovule in its in- 

 side. The fruit {Jig. (3.) is a three-cornered, hard, 

 deep-brown nut, encircled by the calyx, and containing 

 a curved embryo lying on one side of some mealy 

 albumen (fig. 7.), the radicle of the embryo nearly 

 touching the apex of the seed. 



