TRIBES AND SUBTRIBES. 9 



these genera are included by Fournier, as by all others, in one and 

 the same tribe; and if so, are we to regard as the outer glume the 

 small outer one of Panicum, called by some an extra bract, and an 

 imaginary one in Faspalion and its allies, or the outer one of 

 Paspahon, which is second in Panicum2 Again, in one and the 

 same genus the relative position of the outer glume and the main 

 axis is not always constant, as, for instance, in Paspahnn. 



"Another character much insisted on of late years for tribal 

 distinction is still more uncertain, the adherence of the ripe grain 

 or caryopsis to the palea, as in Festuca, Bromus, etc. This is usu- 

 ally very conspicuous in a dry state, and the union is perhaps never 

 truly organic, yet, if not taken too absolutely, the character is 

 sometimes a useful one. 



" Considerable importance was attached by the earlier agrostolo- 

 gists to the presence 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, however, in the lower j^art of the awn in 

 some genera is more constant. The awn, when present, is generally 

 twisted in Andropogoneas, Tristegine^e, Agrostidese, and Avenacese, 

 and not in Panice«, Chlorideae, Festucese, or Hordea?, but there 

 are occasional exceptions. In all the tribes the awn is occasionally 

 deficient. 



" The partial or absolute separation of the sexes or the increase 

 in the number of stamens observed in a few genera have been occa- 

 sionally introduced amongst tribal characters ; but they have 

 proved to be often of no more than generic value, although in the 

 tribe Maydese the absolute unisexuality of the spikelet may be 

 constant. 



''Differences in the size of the embyro, in the form of the so- 

 called scutellum 'on the caryopsis, or in the longitudinal groove or 

 cavity, have been sometimes brought forward as absolute generic, 

 if not tribal, characters, but, as yet, we know too little about them 

 to test their value fairly." 



More recently E. Hackel of Austria has demonstrated the 

 great value of the shape of tlie hilum in defining some of the tribes. 



