Vl] MORPHOLOGY OF AWN 95 



at the base of the true spikelet. In like manner the two 

 paleas are bracteoles which subtend the flower proper. 

 On this assumption they can be compared with the 

 corresponding structures in other plants ; whereas any 

 attempt to compare the paleae or glumes with the sepals 

 and petals of ordinary flowers breaks down. 



A curious interest attaches to the awns so often 

 found on the backs of palese, and especially to those 

 ■where the (sub-terminal) awn springs from just below 

 the bifid apex (e.g. Avena, &c.). 



Hackel showed by comparison with a rolled leaf 

 attached to its sheath and ligule (e.g. Psamma) that 

 such an awn as that of Bromus Alopecurus attached to 

 its palea stands in the relation of a leaf to its sheath, the 

 part of the palea above the insertion corresponding to the 

 ligule, the awn itself to the lamina, and the palea below 

 its insertion to the sheath. This view is rendered the 

 more probable by the anatomy of the awn and by the 

 observations of Schmid, who has shown that the awns of 

 cereals contain chlorophyll-tissue and a vascular bundle, 

 and have stomata, and his experiments led him to con- 

 clude that in the young condition they transpire and 

 assimilate, and probably even contribute to the nutrition 

 of the ripening grain. When dry and mature the awns 

 subserve biological functions of quite another kind, and 

 as we shall see are of importance in the distribution and 

 sowing of the grains. (Fig. 42.) 



Returning to the floral diagram, we see that the two 

 lodicules, the three stamens and the ovary still remain to 



