TAXONOMY OR CLASSIFICATION 155 
ulated above the glumes; spikelets usually laterally 
compressed. 
There are exceptions to all these characters. In some 
cases the exceptional genera are clearly related to others 
that conform to the above definitions. Other genera are 
more or less anomalous and are tentatively placed in the 
category to which they seem most nearly related. In 
Isachne the lower floret is perfect and similar to the 
upper, but it is evidently allied to Panicum and hence is 
placed near that genus in the first series. Several genera, 
such as Sphenopholis, Spartina and Alopecurus, have an 
articulation below the spikelet so that the latter falls 
from the pedicel, in which respect they agree with the 
first series, but in most characters they agree with the 
second series, in which they are placed. In Phalaridez 
of Series II the imperfect florets are below the terminal 
perfect one. 
196. The tribes of grasses.—There are 6 tribes in the 
first series and 7 in the second. The following key to 
these tribes is not made to cover exceptional genera, since 
to do this for the sake of'a comparatively few genera 
would make the keys unnecessarily complex. 
Series [ 
A. oie ig round or dorsally compressed; hilum 
short 
B. Lemmas and palea very thin and hyaline, 
the glumes much thicker. 
c. Inflorescences moneecious, the staminate 
and pistillate flowers in different parts 
of the same plant............ Tribe 1. MaypEax 
cc. Inflorescences not moneecious, usually a (Chap. 15). 
mixture of perfect and staminate or 
neutral spikelets............. Tribe 2. ANDROPOGONE 
BB. Lemmas and paleas membranaceous or (Chap. 16). 
thicker, not thin and hyaline. 
c. Lemmas thinner than the glumes. 
