28 MR. G. BENTHAM ON GRAMINEX. 
The consequence is that there are a considerable number of 
species in whieh the grain has been described by some as ad- 
herent and by others as free, and which have consequently been 
transferred from one genus to another. Yet, if not taken too 
absolutely, the character is sometimes a useful one, assisting, for 
instance, in the arrangement of the genera of some of the sub- 
tribes of the difficult tribe Festucez. 
Considerable importance was attached by the earlier agrosto- 
logists to the presenee or absence of the awn on the back or 
apex of the flowering glume; but this has subsequently been 
found to be subject to great variations. The spiral twist, how- 
ever, in the lower part of the awn in some genera is more con- 
stant,and in the ‘Flora Australiensis’ I had taken it as an essential 
character of some tribes or subtribes ; but there are more ex- 
ceptions than I was then aware of. The awn, when present, 
is generally twisted in Andropogonee, Tristeginex, Agrostide:, 
and Avenacege, and not in Panicer, Chloridem, Festuce&, or 
Horde ; but it is sometimes very slightly so ina few species of 
the latter group, and in the former tribes, where the awn is much 
reduced, if there be any twist it is scarcely perceptible. In all 
the tribes, also, the awn is occasionally, and in the straight- 
awned ones frequently, altogether deficient ; and in some genera, 
as in Stipa for instance, where it is usually twisted, there are 
exceptional species in which it is straight or curved only. The 
character must therefore generally be used with more or Jess 
of reservation. U 
The partial or absolute separation of the sexes or the inerease 
in the number of stamens observed in a few genera have been 
occasionally introduced amongst tribual characters; but further 
observation has shown that they occur amongst Gramine of 
very different aflinities, and have thus proved to be often of no 
more than generic value, although in one tribe, the Maydee, the 
absolute unisexuality of the spikelets may be constant. 
Differences in the size of the embryo, in the form of the so- 
called scutellum on the caryopsis (indicative, apparently, of the 
hilum of the seed), or in the longitudinal groove or cavity fre- 
quently observable on the caryopsis, have been sometimes brought 
forward as absolute generic, if not tribual, characters, and they 
may often be really important; but we know, as yet, too little 
about them to test their value fairly. Herbarium specimens 
rarely supply ripe fruits, and they have been carefully observed 
