18 THE SEEDS OF THE BLUEGRASSES. ~ 
_ Poorly cleaned samples are apt to contain many sterile florets. 
These are slender, sometimes shrunken, and usually lighter colored 
than the grain-bearing florets, which are comparatively plump and 
often dark colored, owing to the color of 
the grain appearing through thé thin palea. 
(Fig. 3.) 
The recognition of the several species of Poa, 
when the identity is questionable, requires the 
use of a good lens and a knowledge of the 
principal distinguishing characters. A sample > 
under examination should be spread thinly on 
ape r, ty u ae 
Fic. 3.—Seeds of Kentucky 
bluegrass (Poa pratensis): a. a Sheet of paper, or, better still, on a black sur- 
in bearing: , sterile. -- 
pone essay ies face. With a good light and means for turn- 
ing the seeds over while under the lens, they can easily be examined 
with reference to size, color, distinctness of veins. character of pubes- 
cence, the condition of the margins of the glume, ete. Exposing the 
different sides of the florets to the light while under examination is 
often absolutely essential in determining the nature of the veins and 
pubescence. 
KEY TO THE SEEDS OF THE MORE COMMON SPECIES OF POA AS FOUND 
ON HERBARIUM SPECIMENS. 
Basal web present. 
Web very persistent and conspicuous ---—----.--2=.--=222------- P. arachnijera. 
Web easily removed, small; keel of the glume pubescent. 
Intermediate veins distinct. 
Intermediate veins sharply defined as narrow ridges; glume margins narrow, 
not easily seen from the side; marginal veins usually smooth- P. trivialis. 
Intermediate veins usually not sharply defined; glume margins broader, easily 
seen from the side in fertile florets; marginal veins pubescent. P. pratensis. 
Intermediate veins indistinct. Se, 
Rachilla segment smooth or nearly so; florets 2-25 mm. long. 
Florets usually broader above than below the middle; apex usually faring; 
rachilla segment smooth ..-...------.--- wpe Ie ee ee eae P. compressa. 
Florets not evidently broader above than below the middle; apex usually 
golden yellow; rachilla segment sometimes rough ---..------- P. triflora. 
Rachilla segment usually pubescent. 
Florets 23-3 mm. long, usually not yellow at the apex. ----- P. nemoralis. 
Basal web not present. 
Florets strongly pubescent. 
Intermediate veins distinct; palea keels prominent, oiten arched forward. 
. P. annua. 
Intermediate veins indistinct; palea keels not arched-----_--------- P. alpina. 
Florets not pubescent —. 222 5-2. 22252 See eee P. sudetiea. 
