30 



Tribe IV.— TKISTEGINE.E. 



Spikelets all hermaphrodite, in panicles; empty glumes three, 

 or the third with a staminate flower in its axil, herbaceous or 

 chartaceous; flowering glumes membranaceous, awned or awnless; 

 rachilla articulated below the empty glumes. 



A small tribe of only seven genera and thirty-three 

 species, natives chiefly of the tropical regions of the 

 Old World. Of the few American species none extend 

 so far north as the United States. 



Tribe V.— PANICE^E. 



Spikelets hermaphrodite, terete or flattened on the back; glumes 

 three or four (rarely only two) ; when four, there is occasionally a 

 staminate flower or a palea in the axil of the third; the upper- 

 most or flowering glume of the hermaphrodite flower is always 

 firmer in texture than the outer glumes, of which the first is 

 usually smaller than the others; axis of the inflorescence not 

 articulated, the rachilla being articulated below the empty glumes, 

 the spikelets falling off singly from their pedicels. 



This is one of the largest tribes in the order Grami- 

 nese. It contains twenty-two genera with over six hun- 

 dred and thirty species. Panicwn, the principal genus, 

 is the largest among grasses, numbering three hundred 

 species. The Panicem are very widely distributed 

 throughout the tropical and temperate regions of the 

 world. Crab grass and the millets are among our best 

 known examples of this tribe. 



KEY TO THE GENERA OF THE PANICEM. 



1. Spikelets unisexual, the staminate in terminal panicles, the fertile 

 on short, leafless, subterranean branches . . 21. Amphicarpum 



1. Spikelets all hermaphrodite 2 



2. Spikelets half imbedded in the flattened axis of the spike-like 



panicle 28. Stenotaphrum 



2. Spikelets not sunken in excavations along the main axis 3 



3. Spikelets subtended or surrounded by one to many bristles or 



spines which are distinct or more or less connate below ... 4 



3. Spikelets not surrounded by a bristly or spiny involucre 6 



4. Bristles or spines falling off with the spikelets 5 



4. Bristles not falling with the spikelets 25. Ch^tochloa 



