SESSILE SPIKELETS IN TWO-SIDED SPIKES 35 



borne at each joint, alternating on opposite sides. 

 The rachis is thickened and the joints slightly hol- 

 lowed on alternate sides. (See Fig. 25, B, a diagram- 

 matic illustration of the rachis seen from the edge 

 with all but two spikelets removed.) 



The spikelet is not very different from that of 

 Bromus (Fig. 11) and as 

 in that, the ripened 

 florets fall from the 

 glumes. 



In the group of 

 grasses taken up in this 

 lesson the specialization 

 is mostly in the rachis 

 and in the position of 

 the relatively simple 

 spikelets. 



In Fig. 26, a spikelet 

 of cultivated w h e a t 

 (Triticum cestivum), we 

 have the same type of 

 spikelet as in Fig. 25 but with fewer and much 

 plumper florets, with broader lemmas slightly toothed 

 at the apex, and with long awns that are scabrous 

 (rough, like a file). [Awns form the " beard" of 

 wheat.] The spikelets are borne on a jointed rachis 

 as in Fig. 25 (Agropyron repens) but the joints are 

 shorter, bringing the spikelets closer together and 

 hiding the rachis. In this, cultivated wheat, the 

 florets do not readily fall from the glumes but re- 



FIG. 26. Spikelet of Triticum cestivum. 



