182 PRINCIPLES OF BOTANY, ETC. 
given for all the natural families, but it is sufficient 
to specify the most important. 
§ 174. 
The Grasses, (§ 122, No. 5), have too great a 
similarity in their whole structure not to make it ne- 
cessary to select particular rules for ascertaining the 
genera. ‘The number of the stamina, the presence 
or want of an arista, can by no means serve either 
for separating or for establishing genera. The num- 
ber of the flowers, of the valves, and of the style, 
however, should not be neglected: there is hardly 
any thing else that affords better distinguishing marks 
than these; and, being steady, if they were to be 
overlooked the genera would grow too large. The 
Involucrum, which is found in some grasses, affords 
various characters that ought not to be rejected, as 
does likewise dee form of the valves and nectaria. 
SIGE 
The Lilies, (§ 122, No, 6), must be distinguished 
by the spatha, according as it 1s one or many-leaved, 
one or many-flowered: and also, which happens in 
few other plants, the stigma, the duration of the co- 
rolla, and the direction of the stamina serve for dis- 
tinguishing genera. We must likewise observe 
whether the stigma be divided, and how often; 
whether the covet falls off, grows dry, or is per- 
sistent; lastly, whether the stamina are erect or bent 
down ; or take an oblique direction. In this, as well 
as in the other natural families, the general rules 
already 
