88 TYPES OF INFLORE'TCENCE [CH. 



The Poa inflorescence is, however, different. It con- 

 sists of a loose branched system of spikelets. Botanists 

 term such a loosely branching system, where each branch 

 ends in a flower, a panicle : here then we have a panicle 

 of spikelets, or, shortly, a Panicle. Aira, Agrostis, Ca- 

 lamagrostis, Avena, Catabrosa (Fig. 4) and many others 

 afford farther examples. 



In Dactylis we have a condition of affairs between the 

 two extremes given: the inflorescence is not so close a 

 spike as Nardus, and not so open a panicle as Poa — it is 

 rather a spike-like panicle, partaking of the nature of 

 both. A special type of this (Foxtail) occurring in certain 

 grasses — e.g. Phleum, Alopecurus, Phalaris and Lagurus, 

 — is so characteristic as to be worth noting (Fig. 3). 



There is also another aspect of these inflorescences 

 which is not without interest as showing how diagnostic 

 characters may be obtained from purely external features, 

 easily observed in the field. We have seen that in 

 Nardus the spikelets are arranged on one side only of 

 the rachis, or main axis, so that about three quarters 

 of the circumference of the latter is bare ; whereas 

 in Lolium — with which Agropyram and Brachypodiimi 

 agree in this respect — the spikelets are on opposite 

 sides, leaving the intervening two quarters, i.e. half its 

 surface, of the circumference of the axis naked. 



In Cynosurus and the simpler forms of Dactylis, we 

 find the spikelets crowded round about three quarters 

 of the surface of the rachis, leaving the fourth quarter 

 naked; and, finally, in Phleum, Alopecurus, Hordewm, 

 and AnthoxantJnim the spikelets cover the entire surface. 



