I 



OF CENTRAL AFRICA. 301 



been expected, in the climates in which tlic collection was 

 formed ; it seems, however, to be connected with the 

 nature of the surfjicc ; for in the Great Desert the reduction 

 of Paniceec is still more remarkable : this tribe l^einjr 

 to Poacca), in that region, in the proportion of only five to 

 eighteen. 



Dr. Oudncy remarks, with respect to the grasses of the 

 desert, that he observed no species with creeping roots ; 

 for a species of Arundo related to Phragmites, which 

 he notices as the only exception, is not properly a desert 

 plant. 



Among the very few Graminese deserving ])articular 

 notice, the first is Avena Porskalii of Vahl. The speci- 

 mens in the herbarium wdiich weve collected in the Desert 

 of Tintuma in some respects differ from all the others that I 

 have seen of this variable species. In the Banksian her- 

 barium there is an authentic specimen from Forskal ; I 

 have received from M. Delile specimens both of ,his A. 

 Forslialii and arundlnacea, described and figured in his 

 'Flore d'Egypte'; and am also in possession of others in 

 somewhat dift'erent states, collected in Egypt by ]\I. Nectoux 

 and Dr. Sieber. From a comparison of all these specimens 

 I am led to believe that A. Forskalii and arundinacea 

 are not specifically distinct ; and it is at least evident that 

 arundinacea more nearly approaches to the plant of 

 Forskal than that to wdiich j\I. Delile has applied the name 

 Forsl:alii. 



This grass, which does not belong to Avena, is referable 

 to Danthonia, from the structure of the outer valve of its 

 perianthium. But Danthonia requires subdivision into 

 several sections, of which, perhaps, our plant may be con- 

 sidered as forming one. 



The character of the section established on Danthonia 

 ForsJialii would chieflj^ consist in the very remarkable obli- 

 quity of the joints of the locusta, which is, indeed, so great, 

 that after their separation each flower seems to have at the 

 base an almost vertically descendent spur ; and as the in- 

 ferior extremity of the up])er joint is produced beyond the 

 lower, a short calcar actually exists before separation, and 



