DESCEIPTIONS OF SPECIES. 23 



Kentucky bluegrass seed is most readily confounded with that of 

 Canada hluegrass {^Poa covipressa) and rough-stalked meadow grass 

 {Poa trivial is). Owing to the difference in cost, Poa compr'essa is 

 sometimes mixed with or substituted for Kentucky bluegrass, while 

 the latter is sometimes similarlj^ emploj^ed with respect to Poa 

 trivial is. 



The characteristic differences between Kentucky blueg-rass seed and 

 that of Canada blueg-rass, as exhibited by the bulk samples and b}" 

 individual seeds under the lens, may be compared as follows: 



Kentucky bluegrass {Poa pratensis) . Canada bluegrass (Poa compressa). 



The usual, well-cleaned bulk samples are Average samples lighter colored than 

 brown in color. those of Kentucky bluegrass. 



Individual, well-matured seeds exhibit The lighter color of individual seeds af- 

 the same brown color of the bulk sam- fords the principal character for the 

 pie. preliminary recognition of these seeds 



in mixtures. 



Nearly all the seeds taper from the cen- Most of the seeds are broader at the apex 



ter to both ends and are not broader at than at the base, often distinctly broader 



the apex than at the base. at the apex than at the middle. 



The apex of commercial seeds is usually Apex of commercial seeds often torn, 



torn, olitusely pointed, keeled, and mostly expanded or flaring, often but 



scarcely hyaline. slightly keeled. 



The intermediate veins are almost in- The intermediate veins are very indis- 



variably distinct. tinct or apparently wanting. 



A number of the sam^^les of Kentucky bluegrass seed examined con- 

 tained seed of the Canada bluegrass. As the latter seed found in com- 

 merce usually contains the prickles or even the seeds of Canada thistle 

 ( Carduus arvensis), these are often found in samples of Kentucky blue- 

 grass seed containing the Canada bluegrass seed. Their presence indi- 

 cates the admixture, since the Canada thistle does not grow in the 

 seed-producing- localities of Kentuck v, while it is abundant in Canada, 

 where the Canada bluegrass is produced. Samples of pure Kentuck}^- 

 bluegrass seed are apt to contain the prickles of horse nettle (Solan um 

 carol inense), sometimes wrongly called bull thistle, a prickly plant 

 common in the bluegrass region of Kentucky. These prickles are 

 similar to those of the Canada thistle, but ma}" be distinguished, as 

 shown hereafter in this paper in describing- the impurities of the blue- 

 g-rass seeds. The fact that Canada bluegrass onl}' begins to flower at 

 the time Kentucky bluegrass is ripe precludes the possibility of the 

 mixture of the two kinds of seed owing to the fact of growth together. 

 Such mixture can occur only after the seed is gathered, through acci- 

 dent or intent. 



