C4RAMINE^ 



433 



In some of the species the points of the roots are 

 covered with hard scales, which enables them to force 

 their way. The common Couch-grass has thus been 

 known to bore through the roots of trees. 



Fig. 348. — Transverse section of half of leaf of Poa annua including the median 

 keel. X about 50. Six vascular bundles are represented in the half of the 

 blade, the strongest one is girdered with Kclerenchyma. m, lines of motor cells 

 on upper face above the median vascular bundle. 



The flowers of Grasses have as a rule definite hours 

 for opening. Poa, Kceleria, and Avena elatior take the 

 lead between 4 and 5 a.m. ; Briza media, Aira ccespitosa, 

 and Barley, are a little later, between 5 and 6 ; a good 

 many species, Rye, some Festucas, Andropogon, Dactylis, 

 between 6 and 7 ; Alopecurus, Phleum, and Antho- 

 xanthum, between 7 and 8. Then 

 comes an interval. At 1 1 Agrostis 

 opens ; between 12 and 1 Melica, 

 Molinia, Nardus, Elymus, Sclero- 

 chloa, and some species of Calam- 

 agrostis. Some species of Bromus 

 open about 2, some of Avena 

 about 3, Agropyrum at 4, and, 

 lastly, Aira Jlexuosa between 5 

 and 6. Holcus is peculiar. It 

 opens under favourable circum- 

 stances twice, at 6 in the morn- 

 ing, and 7 in the evening. Each 

 flower takes from 15 to 20 

 minutes. 



Wheat is said to open at any time of the day. The 

 anthers scatter about two -thirds of their pollen, and 

 drop one-third in their own flower, which, however, 

 gives better results if cross-fertilised. Rye is said to be 

 quite sterile to its own pollen. 



2 F 



Fig. 349. — Transverse section 

 of leaf of Nardus stricta. 

 X about 50. The shaded 

 portions represent support- 

 ing tissue (sclerenchyma). 

 in, traces of motor cells 

 at base of furrow in upper 

 face. 



