108 A TEXT-BOOK OF GRASSES 



taspis) present arcuate nerves diverging at the base and 

 converging at the apex, with numerous often conspicuous 

 cross-veins, thus simulating the so-called netted-veined 

 blades of dicotyledons. 



Besides the various genera already mentioned as having broad 

 blades are the following which also present well-marked cross-veins: 

 Olyreae, Centhotheca, Senites, Orthoclada, Pariana, many bamboos, 

 and a few other genera. Pharus differs in having straight parallel 

 lateral nerves that diverge from the midrib nearly throughout its 

 length and join with a strong marginal nerve, instead of converging 

 at the apex (Fig. 29). Leptaspis resembles Pharus, but Strepto- 

 chaeta is intermediate. 



138. Auricles. — Some grasses bear, one on either side at 

 the base of the blade, appendages known as auricles. 

 These auricles are characteristic of the tribe Hordese and 

 are found in certain species of other tribes. 



Wheat, rye and barley show prominent auricles. Rice and 

 Festuca elatior and its allies are examples outside the Hordeae. A 

 very unusual development of the blade is shown in Phyllorachis 

 sagittata Trim, and Spodiopogon sagittifolius Rendle. The base of 

 the blade is extended into a long lobe on either side of the short 

 petiole. 



139. Roll-leaves. — In a preceding paragraph (Par. 

 136), casual mention was made of blades in which, by 

 rolling in various ways, the exposed surface is reduced. 

 This rolling of the blade is a xerophytic character and 

 tends, by reduction of the evaporating surface, to lessen 

 the loss of moisture. Such reduction of surface is charac- 

 teristic of grasses of plains and desert regions, of sandy soil, 

 especially along the seacoast, and of saline marshes. In 

 some cases the blades are permanently rolled, in other 

 cases they are flat under favorable conditions of atmos- 

 pheric moisture but readily roll when the moisture 



