Natural Orders .] APPENDIX. 581 
teration first takes place in the inner or upper valve ; but this valve having, 
instead of one central nerve, two nerves equidistant from its axis I consi- 
der it as composed of two confluent valves, analogous to what takes place 
in the calyx and corolla of many irregular flowers of other classes; and 
this confluence may be regarded as the first step towards its obliteration, 
which is complete in many species ofPanicum, in Andropogon, Pappopho- 
rum, Alopecurus, Trichodium, and several other genera. 
With respect to the nature of this inner or proper envelope of 
o-rasses, it may be observed that the view of its structure now given, in 
reducing its parts to the usual ternary division of Monocotyledones, affords 
an additional argument for considering it as the real Perianthium. I his 
argument, however, is not conclusive, for a similar confluence takes place 
between the two inner lateral bracteoe of the greater part of Iridese ; and 
with these, in the relative .insertion of its valves, the proper envelope of 
grasses may be .supposed much better to accord, than with a genuine Pe- 
rianthium. If therefore this inner envelope of grasses be regarded as 
consisting merely of bracteae, the real Perianthium of the order must be 
looked for in those minute scales, which in the greater part of its genera 
are found immediately surrounding the sexual organs. 
These scales are in most cases only two in number, and placed 
collaterally within the inferior valve of the proper envelope. In their real 
insertion, however, they alternate with the valves of this envelope, as is 
obviously the case in Ehrharta and certain other genera ; and their collate- 
ral approximation may be considered as a tendency to that confluence 
which uniformly exists in the parts composing the upper valve of the pro- 
per envelope, and which takes place also between these two squamae them- 
selves, in some genera, as Glyccria and Melica. In certain other genera, as 
Bambusa and Stipa, a third squamula exists, which is placed opposite to 
the axis of the upper valve of the proper envelope, or, to speak in confor- 
mity with the view already taken of the structure of this valve, opposite to 
the junction of its two component parts. With these squamae the stamina 
in triandrous grasses alternate, and they are consequently opposite to the 
parts of the proper envelope; that is, one stamen is opposed to the axis of 
its lower or outer valve, and the two others arc placed opposite to the two 
nerves of the upper valve. Hence, if the inner envelope be considered as 
