CH. VIIl] 



'SEED -CHAEACTERS 



127 



America, Aristida hygrometrica in New Zealand, Hetero 

 pogon contortus in New Caledonia. 



The driving action of even small 

 reflexed asperities on awns is well 

 illustrated by the fruits of Hordeum, 

 which are often made by children to 

 creep up the sleeve. 



When we come to examine the 

 external features of the "seeds" of 

 grasses — usually the caryopsis en- 

 closed in one, or more palese, but 

 sometimes in glumes as well — the 

 following diagnostic characters are 

 of importance. 



The size varies from lengths of 

 2 mm. or less (Poa, Aira) (Figs. 43, 

 44) to 15 — 20 mm. or more {Arrhe- 

 natherum) (Fig. 47) and distinction 

 must be made between the various 

 characters of the caryopsis devoid of its coverings (palese, 

 glumes) and such as really belong to the latter. 



The caryopsis proper may be short and stout and 

 devoid of a groove — " Millet-seed " type (Fig. 45) — but is 

 oftener elongated, like a grain of Wheat, and then has 

 the characteristic longitudinal groove on the face opposite 

 that where the embryo is situated (Fig. 46). Details of 

 shape — e.g. cylindroid, fusiform, flattened, &c. — are also of 

 diagnostic value. 



In many cases the " seed," consisting of the caryopsis 

 closely compressed between the paleee, is boat-shaped, e.g. 



Fig. 43. Poa annua. 

 d, the " seed," nat. 

 size; a and 6, ditto, 

 X about 7 ; c, cary- 

 opsis, natural size 

 (above) and x about 

 7. Note the ribs 

 and silky keel. No 

 "web." Nobbe. Cf. 

 Figs. 54—56. 



