BULLETIN 406, U. S. DEPAETMENT OF AGRICULTURE. 



DISTINGUISHING CHARACTERS OF THE SEEDS OF JOHNSON GRASS. 



Jolmson grass seeds in tlie hull (fig. 4, 1) vary in length from fifteen 

 one-hundredths to twenty-two one-hundredths of an inch. Most of 



the seeds have a smooth, 

 rounded, and light- 

 colored scar at the base. 

 The appendages of the 

 seed (fig. 4, h) are mostly 

 entire, expanded, cup 

 shaped, and smooth at 

 the apexes, correspond- 

 ing with the scar at the 

 base of the seed. The 

 uniformly smooth border 

 of the expanded, cup- 

 apex, together 

 separation of the 



Fig. 4.— Johnson grass seeds, enlarged. IT nhulled seeds, spLkelets 

 (1); hulled grains (2): a, a, Scar of the hull; 6, b, appendages of 

 the seed with expanded, cup-shaped apexes; c, scar of the grain; 

 d. embryo. 



shaped 

 with the smooth seed scar, results from the norma' 

 seed along a definite suture. 



The prevailing color of mature seed hulls is 

 blackish brown. Many seeds are partially or 

 wholly reddish. Some are straw colored. A few 

 are tawny or light brown. 



The hulled grains (fig. 4, 2) vary from eight 

 one-hundredths to twelve one-hundredths of an 

 inch in length. They usually are oval, sometimes 

 oval-elliptical in outline, the embryo end tending 

 to be the more pointed. The color is dark reddish 

 brown. They are noticeably smaller and darker 

 colored than those of Sudan grass and have a 

 relatively narrower embryo (fig. 4, d). 



APPARENT EXCEPTIONS TO THE DISTINGUISHING 

 CHARACTERS DESCRIBED. 



Conflicting conditions arise from exceptions in 

 the manner of the fall of the seeds of Sudan grass 

 and Johnson grass. 



Occasional Sudan grass seeds have no stem at 

 the base, but the scar usually is irregular or jagged, 

 owing to the absence of a definite suture. Like- 

 wise, some seeds have one or both appendages 

 unbroken, with expanded and occasionally cup-shaped apexes. The 

 size of the seed, together with the size, form, and color of the grain, 

 should suffice to distinguish the seed from that of Johnson grass. 



Fig. 5. — Stem-hearing seeds 

 of Johnson grass, enlarged: 

 (1) A seed in which the 

 stem (a) is a portion of a 

 rachis segment. The sut- 

 ure (h) at the junction of 

 the stem and seed is evi- 

 dent. (2) A seed (the 

 lowest of the cluster) in 

 - which the longer stem (c) is 

 a part of the cluster branch. 

 Ko suture occurs at the 

 junction {d) of the branch 

 and the first rachis seg- 

 ment {e). The opposite 

 side of such a seed shows 

 the suture, as at 6. 



