TlilBES AND SUBTRIBES. 9 



these genera are incliuled by Fournler. as by all others, in one and 

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

 small outer one of Paiiiruin, ealled by some an extra bract, and an 

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

 I'tis/Kf/K/ti, which is second in Paiiicuin? Again, in one and the 

 same genus the rehitive position of the outer glume iind the main 

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



" Another character much insisted on of late years for tribal 

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

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

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

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

 sometimes a useful one. 



•' Considerable inii)ortance was attached by tlie earlier agrostolo- 

 gists to the presence or absence of the awn on the back or ajjcx of 

 the (lowering glume: l)ut this has subsequently been found to be 

 subject to great variations. 



••The spiral twist, however, in the lower part of the awn in 

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

 twisted in .\ndropogonea>. 'I'risteginea". Agrostidea-. and Aveiiacete. 

 and nut in I'anicea'. Chlorideas Fcstucea'. or llordea". but tliere 

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

 deficient. 



•'The [>artial or al)solute separation of the sexes or the increase 

 in Ihe number of stamens observed in a few genera have l)een occa- 

 sionally introduced amongst tribal characters ; but they have 

 proved to be often of no more tlian generic value, although in tlie 

 tribe Maydeie the absolute unisexuality of the gpikelet may be 

 constant. 



•• Ditferences in the size of the embyro, in the form of the so- 

 called scutellum on tiie 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 H. Haekel of Austria has demonstrated the 

 great value of the shai)e of the liilum in detining some of the tribes. 



