=Slender Pigweed.= _Amaranthus hybridus_ L. (_A. chlorostachys_). Seeds smooth, highly polished, jet-black, double convex, broadly ovate, with a slight notch at the narrow extremity, 1.1-1.4 mm. long. Distinguished from the preceding species by having a seed ovate instead of circular. Introduced from tropical America. Not abundant. [Illustration: Fig. 58.] =Rough Pigweeds.= _Amaranthus retroflexus_ L. Sometimes incorrectly called red-root. Seeds smooth, highly polished, jet-black, double convex, broadly ovate, with a slight notch at the narrow end, .9-1.2 mm. long. The seeds of this and the next preceding are ovate, while those of the first two are very nearly circular. When seen edgewise, the hem-like margin of this seed is less prominent then in either of the preceding three noticed above. Found almost everywhere in annual crops. Introduced from tropical America. KNOTWEED FAMILY. ILLECEBRACEAE. [Illustration: Fig. 59.] =Knawel.= _Scleranthus annuus_ L. As the seed is single for each flower, it is unnecessary for the ovary to open; the small, hardened, ten-angled calyx with its five thick lobes aid in protecting and distributing the seed within. The seed is seldom seen. Calyx straw colored, obovoid, 2 mm. long besides the five spreading, membranaceous lobes, which are nearly as long. A low spreading plant, resembling some kinds of chickweed. AIZOACEAE. [Illustration: Fig. 60.] =Carpet-Weed.= _Mollugo verticillata_ L. Seeds orange-red, shining, flattened, kidney-shaped or ovoid, .4-.6 mm. long, concave on the thinner edge from which protrudes a nipple-like point, a low central ridge passing over the rounded edge. Native of warmer America. Needing sand. PINK FAMILY. CARYOPHYLLACEAE. [Illustration: Fig. 61.] =Cockle.= _Agrostemma Githago_ L. Flowers rose-colored; pod erect, ovoid, about 16 mm. long; seeds dark brown to black, wedge-shaped-triangular, appearing as though the two extremities were bent together; surface covered with curved rows of conspicuous teeth, one side 3-3.5 mm. long. Introduced from Europe. In no sense a weed except in wheat fields. [Illustration: Fig. 62.] =Thyme-leaved Sandwort.= _Arenaria serpyllifolia_ L. Flowers white; seeds reddish brown to lead color, slightly flattened, circular to short-kidney-shaped. Each side covered with 4-5 curved rows of smooth, oval tubercles, giving the appearance of having two extremities bent together, about 5 mm. in diameter. Naturalized from Europe, delighting in light, poor soil. When well grown it becomes a tumbleweed. [Illustration: Fig. 63.]