Pipei — Andropogon halepensis and Andropogon sorghum. 31 



Arabian varieties with flat white seeds and villous glumes, one of which 

 is surely the same as or very similar to white durra. 

 Andropogon sorghum Brot. Fl. Lusit. 1:88. 1804. Based on Holcus 

 sorghum L. 



Andropogon sorghum is best differentiated from A . halepensis by the 

 absence of rootstocks. All other characters tliat have been used break 

 down completely. Thus the persistence of the spikelets in Andropogon 

 sorghum as contrasted with their ready disjunction in Andropogon hale- 

 pensis does not hold in several of the wild races {virgatus, eichingeri, 

 verticilliflorus) and in some cultivated varieties the spikelets also shatter 

 readily. 



Andropogon sorghum is a much more diverse species than is ^. hale- 

 pensis. The species so far as the wild forms are concerned is apparently 

 limited to the African continent south of the Sahara Desert, except in 

 Egypt where it occurs to the mouth of the Nile, and Madagascar and the 

 neighboring islands. In Tahiti occurs a race known as Toura grass not 

 identified with any of the African sub-species, but it is doubtful if Toura 

 grass is native in Tahiti. Still more doubtful is the scanty material from 

 Australia. Some of the Australian specimens are undoubtedly introduced 

 A. halepensis, but otiiers scantily represented are not identified with any 

 known form of either A. sorghum or A. halepensis. It is therefore pos- 

 sible that races of Andropogon sorghum are native to Australia and even 

 to Tahiti. 



Eleven wild races or subspecies are here described. Tlie more marked 

 of these such as exiguus, hewisoni and vogelianus are very distinct, but 

 others such as sudanensis, verticilliflorus and effusus seem connected 

 by intermediate forms. It is entirely probable when ample material is 

 available from the vast continent of Africa, that many more often illy 

 defined races will be found to occur. It is perfectly clear that the species 

 as a whole is a remarkable assemblage of races and that much further in- 

 vestigation is necessary to determine definitely which of these races were 

 brought into cultivation by the negroes thus giving rise to the long series 

 of cultivated varieties. 



Key to the Wild Subspecies op Andropogon sorghum. 



Culms slender, rarely exceeding 6 mm. in diameter; sheaths mostly 

 shorter than the internodes ; panicles loose. 



Panicle long and narrow, the rays strongly ascending or nearly erect. 

 Lower glume of fertile spikelet narrowly lanceolate, 9-11 nerved, 



nearly glabrous on the back .... exiguus. 



Lower glume of fertile spikelet ovate-lanceolate, 7-9 nerved, very 



hairy eichingeri. 



Panicle broad, the rays spreading. 



I^af-blades narrow, rarely as much as 15 mm. broad; panicle 

 branches ascending-spreading; lower glume 6-7 mm. long, nearly 



glabrous on the back sudanensis. 



Leaf-blades broader, often 2-3 cm. wide. 



