GRASSES OF IOWA. 



the spikelets or cluster of spikelets and the single perfect flower, which 

 may or may not have a staminate or imperfect flower below it. There 

 are never more than four glumes in the spikelets, the first three being 

 empty or the third with a rudimentary or staminate flower in its axil; 

 the fourth glume subtends the perfect or hermaphrodite flower. In a 

 few genera the spikelets are reduced to two or even only one glume, but 

 in these cases the articulation of the spikelet with the pedicel below the 

 outer glume indicates its connection with this series. 



KEY TO THE TRIBES IN SERIES A. — PANICACEAE. 



i. Spikelets usually much compressed laterally, i-flowered; empty glumes 

 none or rudimentary; flowers staminate, pistillate, or hermaphrodite. 



—TRIBE VI. ORYZEAE. 



2. Spikelets either staminate or pistillate, each in a separate inflorescence 

 on the same plant, or in distinct parts of the same inflorescence. 



—TRIBE I. MAYDEAE. 



3. Spikelets either all hermaphrodite or hermaphrodite and staminate, regu- 

 larly arranged and usually in pairs, one sessile, the other pedicellate in the same 

 inflorescence (both pedicellate in Trachypogon). 



—TRIBE II. ANDROPOGONEAE. 



4. Spikelets in groups of two to six at each joint of the main axis, each 

 group falling off entire; flowering glumes usually awnless. {Cathestechum may 

 be looked for here.) TRIBE III. OSTERDAMIEAE. 



5. Flowering glumes of the perfect flowers membranaceous and (in Amer- 

 ican species) awned TRIBE IV. TRISTEGINEAE. 



6- Flowering glumes of the perfect flower cartilaginous, coriaceous or char- 

 taceous and awnless or (in Eriochloa) with a short, straight awn. 



—TRIBE V. PANICEAE. 



SERIES B.— POACEiE. 



Spikelets one to many-flowered, the imperfect or rudimentary 

 flower, if any, usually uppermost; rachilla usually articulated above the 

 empty glumes, so that these remain after the fall of the fruiting glumes. 1 

 In spikelets with two or more flowers these are separated by a mani- 

 fest internode of the rachilla, and in such cases the rachilla is usually 

 articulated below each flowering glume. 



In this second grand division of the Gramineae the pedicels are not 

 (or are very rarely) articulated below the outer glumes, but the axis of 

 the spikelet is articulated above these glumes, so that they usually remain 

 attached to the pedicel after the falling off of the mature florets. The 

 spikelets are one to many-flowered, and have as many flowering glumes 

 as there are flowers; the imperfect flowers, when present, are the upper- 

 most; the terminal floret may be staminate or rudimentary. 



1 In Alopecurus, Cinna, Spartina, Beckmannia and JTolcvs the rachilla is articulated 

 below the empty or outer glumes, and the spikelets fall off entire. 



