DESCRIPTIONS OF SPECIES. ies 
Kentucky bluegrass seed is most readily confounded with that of 
Canada bluegrass (Poa compressa) and rough-stalked meadow grass 
(Poa trivialis). Owing to the difference in cost, Poa compressa is 
sometimes mixed with or substituted for Kentucky bluegrass, while 
the latter is sometimes similarly employed with respect to Poa 
trivialis. 
The characteristic differences between Kentucky bluegrass seed and 
that of Canada bluegrass, as exhibited by the bulk samples and by 
individual seeds under the lens, may be compared as follows: 
KENTUCKY BLUEGRASS (Poa pratensis). 
The usual, well-cleaned bulk samples are 
brown in color. 
Individual, well-matured seeds exhibit 
the same brown color of the bulk sam- 
ple. 
Nearly all the seeds taper from. the cen- 
ter to both ends and are not broader at 
the apex than at the base. 
The apex of commercial seeds is usually 
torn, obtusely pointed, keeled, and 
scarcely hyaline. 
The intermediate veins are almost in- 
variably distinct. 
CANADA BLUEGRASS (Poa compressa). 
Average samples lighter colored than 
those of Kentucky bluegrass. 
The lighter color of individual seeds af- 
fords the principal character for the 
preliminary recognition of these seeds 
in mixtures. 
Most of the seeds are broader at the apex 
than at the base, often distinctly broader 
at the apex than at the middle. 
Apex, of commercial seeds often torn, 
mostly expanded or flaring, often but 
slightly keeled. 
The intermediate veins are very indis- 
tinct or apparently wanting. 
A number of the samples 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 dees not grow in the 
seed-producing localities of Kentucky, while it is abundant in Canada, 
where the Canada bluegrass is produced. Samples of pure Kentucky 
bluegrass seed are apt to contain the prickles of horse nettle (Solanum 
carolinense), 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 may be distinguished, as 
shown hereafter in this paper in describing the impurities of the blue- 
grass seeds. The fact that Canada bluegrass only 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. 
