22 Botanical Section [PT i 



blades are thin, flat, and have stomata freely exposed on both 

 surfaces, e.g. Brachypodium sylvaticum. 



Very little is known of the functions of the ligule and auricles, 

 and they appear to be unimportant physiologically. Possibly 

 they may serve to shoot off the water as it runs to the base of 

 the blade and so prevent it from getting into the sheath. 



Pollination. When the reproductive organs are mature the 

 lodicules swell and push apart the paleae, thus exposing the 

 stigmas which are now spread to their fullest extent. About the 

 same time the filaments of the stamens, which have up till now 

 remained very short, rapidly elongate and carry out into the air 

 the dangling anthers, which burst and shed abundance of pollen. 

 In some cases the stigmas are mature and ready for pollination 

 before the pollen of the same flower is ripe, e.g. Meadow Foxtail, 

 but in most cases the pollen is ripe and begins to be shed before 

 the stigmas of the same flower are mature. 



The feathery nature of the stigmatic plumes, their size and 

 spreading position, together with the large quantities of pollen 

 produced, indicate that wind is the principal agent in the cross- 

 pollination of the flowers. In some species however, e.g. wheat, 

 barley, etc., the flowers are cleistogamous, i.e. pollination 

 and fertilisation are accomplished before or even without the 

 opening of the paleae. In such cases cross-fertilisation is normally 

 impossible. 



The dissemination of grass "seeds" is probably much facilitated 

 by the attached glumes (Holcus, Alopecums, etc.), inflated 

 paleee (Briza, etc.), or by the silky hairs at the base of the "seed" 

 ("web" in Poa sps.), or on the rachilla (e.g. Arundo, Wild Oat, 

 etc.), each of which are aids to their distribution by wind. See 

 Figs. 45, 52, 58, 62, 114, 126 and 142. 



Bristles and barbed awns (e.g. Barren Brome) also serve to 

 fasten the "seeds" to animals. Again, the hardened base of 

 many grass "seeds," the presence of bent or twisted awns (False 

 Oat), and the position occupied by the hairs all assist in burying 

 the "seed" in the soil in order that it may germinate. Figs. 55 

 and 74. 



