580 APPENDIX. [ Botany of Terra Australis. 
consists merely of the squamae of a spicula, similar to that of Kyllinga, but 
reduced to two valves. 
GRA M IN E E. This order comprehends, at least, one- fourth of the 
whole of Monocotyledones, and in Terra Australis, where upwards of 200 
species have already been observed, it bears the same proportion to that 
primary division. 
I have formerly, in arranging the Australian genera of Graminece , en- 
deavoured to explain what I conceived to be the natural subdivision of 
nearly the whole order into two great tribes. The reasons which I then 
assigned for this arrangement appear, however, either not to have been 
comprehended, or to have been considered too hypothetical. With a view 
of removing the supposed obscurity and strengthening my former argu- 
ments, I shall preface what I have now to say on the subject, by a few 
observations common to both tribes. 
The natural or most common structure of Graminece is to have their 
sexual organs surrounded by two floral envelopes, each of which usually 
consists of two distinct valves : but both of these envelopes are in many 
genera of the order subject to various degrees of imperfection or even 
suppression of their parts. 
The outer envelope or Gluma of Jussieu, in most cases, containing 
7 o 
several flowers with distinct and often distant insertions on a common 
receptacle, can only be considered as analogous to the bractete or involu- 
cram of other plants. 
The tendency to suppression in this envelope appears to be greater in 
the exterior or lower valve, so that a gluma consisting of one valve may, 
in all cases, be considered as deprived of its outer or inferior valve. In 
certain genera with a simple spike, as Lolium and Lcpturus, this is 
clearly proved by the structure of the terminal flower or spicula, which 
retains the natural number of parts ; and in other genera not admitting of 
this direct proof, the fact is established by a series of species shewing its 
gradual obliteration, as in those species of Panicum which connect that 
genus with Paspalum. 
On the other hand, in the inner envelope or Calyx of Jussieu, obli*» 
