WEED SEEDS FOUND WITH BLITEGRASS SEEDS. 



33 



concentric rows on the similar faces; color brown, or reddish in immature seeds: 

 embryo cyhndrical, curved about the endosperm, its extremities nearly meeting at 

 the scar. (Fig. 19, a.) 



Alsine media is very common in the United States, but is so low-growing that the 

 American method of seed stripping prevents the occurrence of its seeds in abundance 

 in commercial bluegrass seeds. Its seeds 

 are common in European bluegrass seeds, 

 particularly those of rough-stalked meadow 

 grass. 



Alsine graminea ( L. ) Britton. 



a b c 



Fig. 19.— Seeds of chickweeds: o, Alsine me- 

 dia; b, A. graminea; c, natural size of seeds. 



Seeds similar to those of Alsine media, ex- 

 cept in form and surface markings; usually 



circular or oval; faces and edges somewhat rounded, finely roughened by short, inter- 

 lacing ridges which are arranged more or less concentrically on the faces and 

 parallel on the edges; surface dull; color grayish-brown, immature seeds reddish. 

 (Fig. 19, h.) 



Not found in American seed; frequent, although not abundant, in European seed. 



a 



6 



Carduus arvensis (L. ) Eobs. 



CANADA THISTLE. 



Fig. 20.— Seeds of Canada thistle ( Carduus arvensis) : a, well- 

 matiired seeds; 6, natural size of seeds; c, a shriveled seed. 



Seeds (akenes) 2-3 mm. long, 

 oblong-lanceolate, flattened with 

 obtuse edges, slightly ridged along 

 each face, straight or curved edge- 

 wise, sometimes face wise; apex 

 truncate, often obliquely so, con- 

 cave with a ring-like border; corolla scar represented by a central, conical projection; 

 surface dull and mostly smooth, sometimes with several narrow, longitudinal grooves; 

 color brown, the apical margin usually lighter 

 and sometimes yellowish. (Fig. 20.) 



Prickles of Canada thistle and horse nettle 

 {Solanum carolinense) often occur in certain 

 bluegrass seeds. While the presence of the 

 former is significant with respect to adultera- 

 tion, the two kinds are apt to be confounded. 

 The prickles of Canada thistle are 2-6 mm. 

 long, veryslender, yellowish, usually expanded 

 and laterally flattened at the base, which con- 

 sists of a portion of the leaf tissue and is darker 

 colored than the rest of the prickle, somewhat 

 rounded or angular in form and jagged-edged. 

 (Fig. 21, cand d). 



The prickles of horse nettle {Solanum caro- 

 linense) are coarser, 4-8 mm. in length, light 

 yellow in color, u.^ually not darker at the base. 

 They are produced on the stems and the coarse 

 midribs of the leaves, and on breaking off have 

 a transversely flattened scar. They occur fre- 

 quently in samples of Kentucky-grown Poa pratensis and are easily mistaken for 

 those of Canada thistle. (Fig. 21, a and b. ) 



Matured seeds, shriveled seeds, and prickles from the leaves and stems of Canada 

 thistle are frequently found in Canada bluegrass seed. The presence of the prickles 



C ^^Z 



Fig. 21.— Prickles often found with blue- 

 grass seed: a and b, horse nettle (Hola- 

 num carolinense) enlarged and natural 

 size; c and d, Canada thistle (Cardans 

 or)'e?isis) enlarged and natural size; 1 and 

 2, characteristic forms of the bases of 

 the two kinds of prickles. 



