30 



FIRST BOOK OF GRASSES 



rachilla does not disarticulate, the sterile florets re- 

 maining permanently attached to the fertile one, the 

 numerous awns of all together forming a pappus-like 

 crown which carries the seed before the wind. [Pap- 

 pus is the "down" on the seed of a dandelion, thistle, 

 or other plant of their family.] 



Next we shall examine the inflorescence of a grass 

 having spikelets entirely of sterile florets in addition 



to spikelets of fer- 

 tile flprets. Ex- 

 amine Fig. 21, A 

 {Cynosurus crista- 

 tus), which shows 

 a small part of a 

 spike-like panicle. 

 The spikelets are 

 borne on minute 

 pedicels on very 

 c, fertile short compound 

 branches. The 

 lower one to three spikelets of each little branch 

 are sterile, the lemmas containing no flowers (Fig. 

 21, B). The upper one to three spikelets are smaller 

 and fertile (Fig. 21, C). When the bracts of the 

 sterile spikelet are all ahke empty, why are all 

 but the lower pair called lemmas, instead of glumes? 

 In many cases the nature of modified organs can 

 only be recognized by their correspondence to or- 

 gans in the same relative position in allied but 

 more simple forms. In all the spikelets examined 



Fig. 21. A, part of a panicle of Cynosuru; 

 cristatus; B, sterile spikelet; 

 spikelet. 



