PEDICELED ONE-FLOWERED SPIKELETS 47 



let of Agros- 

 tis hiemalis. 



the palea also is suppressed or represented by a 

 rudiment only (Fig. 36, Agrostis hiemalis, the floret 

 with palea wanting, raised from the 

 glumes). Here we have specialization 

 through elimination, the spikelet reduced 

 almost to its lowest terms, one floret 

 with no palea, no awn, no callus hairs. 

 In this particular species the very open 

 panicles break off and roll before the 

 wind as tumbleweeds, scattering the fig.36. Spike- 

 seed. Several species of Agrostis have 

 awned lemmas and some have callus 

 hairs, shorter and less copious than in Calamagrostis. 

 In Sporobolus (Fig. 37, the floret raised from the 

 glumes and containing a mature grain) 

 the nerves of the palea are wide 

 apart and the internerve (the space 

 between the nerves) is thin in texture 

 and readily splits as the grain matures. 

 In some species it splits to the apex, 

 resulting in an object sorely puzzling 

 to the beginner, the two halves appear- 

 ing like two 1-nerved lemmas or paleas, 

 in addition to the lemma itself. It is 

 Fig. 37. Spike- in such cases as this that a knowledge 

 let of Sporo- f fae structure of the grass spikelet is 



bolus airoiaes. ° g x 



necessary for the correct interpretation 

 of the organs observed. In this genus and in a few 

 others the pericarp (meaning around the fruit), the 

 wall of the ripened ovary which forms a covering 



