52 FIRST BOOK OF GRASSES 



In Stipa the awn is composed of all the nerves of 

 the lemma, forming a solid slightly flattened elongate 

 body, the point of departure from the body of the 

 lemma being marked by an abrupt contraction or a 

 ring of hairs. In some species the lower part of the 

 awn is plumose (covered with soft fluffy hairs, like a 

 feather). 



In Aristida the awn is divided into three; that is, 

 the three nerves at first unite, then separate. The 

 lemma tapers into the awn with no visible junction, 

 as in Stipa. Sometimes the undivided part of the 

 awn is elongate, forming a slender neck and some- 

 times this neck is twisted. In Aristida dichotoma, 

 the species shown (Fig. 46), the lateral awns are much 

 shorter than the central one. In many species the 

 three are subequal, and one or all may be recurved or 

 loosely twisted at the base. They are never tightly 

 twisted, as in Stipa. 



SUMMARY 



The specialization in this group of grasses con- 

 sists in the reduction of the relatively simplified 

 spikelet to a single floret. In most of the genera the 

 spikelets are very small. The glumes may be re- 

 duced to rudiments or suppressed or may be well 

 developed and somewhat elaborated. The lemma 

 may be delicate or indurate (hardened) and may be 

 awned from the back or the summit. The palea 

 shows more modification in this group than in any 

 other. It may be suppressed or it may be as long as 



