COMPARATIVE ANALYSIS. 



237 



AVENA. Florets with two long bristles at summit . Strigosa. 



Florets without bristles at summit . . Fatua. 



CYNOSUEUS. Outer palea terminating in a short awn, not 



half length of palea . . Cristatus. 

 Outer palea terminating in a long awn, as 



long as the palea . . EcUnatm. 



POA. Florets webbed .... 1 



Florets not webbed . . . .4 



1. Upper leaf much longer than sheath . . 2 

 Upper leaf about as long or longer than sheath . 3 



2. Ligule of upper sheath short and rounded . Pratensis. 

 Ligule of upper sheath long and pointed . . Trivialis. 



3. Ligule scarcely perceptible, outer palea five-ribbed . Nemoralis. 

 Ligule prominent, outer palea three-ribbed . Compressa. 



4. Florets hairy at base .... 5 

 Florets not hairy . . . .12 



5. Outer palea three-ribbed ... 6 

 Outer palea five-ribbed . . . .7 



6. Panicle erect, upper leaf linear, folded ' . . Alpina. 

 Panicle drooping, upper leaf lanceolate, flat . . Laxa. 



7. tipper joint situated above centre of stem . 8 

 Upper joint situated below centre of stem . . 9 



8. Second sheath not reaching to first joint . . Poly no Aa. 

 Second sheath extending beyond first joint . Montana. 



9. Small glume reaching beyond base of third floret . 10 

 Small glume not reaching beyond base of second floret 11 



10. Eachis and branches rough . . . C&sia. 

 Eachis and branches smooth . . . Annua. 



11. Eachis and branches rough to touch . . . Distans. 

 Eachis and branches smooth to touch . . Maritima. 



12. Glumes with a prominent lateral rib on each side Procumlcns. 

 Glumes without lateral ribs . . . 13 



13. Lower half of central rib of outer palea smooth . 14 

 Central rib of outer palea rough the whole length . 15 



14. Summit of upper glume reaching to base of third floret Rigida. 

 Summit of upper glume reaching to base of fourth floret Loliacea. 



15. Outer palea three-ribbed . . . Sykatica. 

 Outer palea seven-ribbed . . . 16 



16. Panicle compound, spikelets not a quarter of an inch in 



length . . Aquatica. 



Panicle simple, spikelets an inch in length . Fluitans. 



