FRUITS AND COLONISATION BY SEED. 5 I 



In, for instance, Stipa capillacea, the awn is very sen- 

 sitive to even slight changes in the moisture of the 

 atmosphere. If it should happen to fall on a sheep's 

 back the free end of the awn catches on the wool, and as 

 it twists and untwists, must force the sharp point at the 

 base of the glume into the skin ; the rigid hairs alluded 



Fig. 5.— Hygroscopic Awns, (i) Harestail Grass {Lagurtis). (2) Stipa spine. 

 (3) Storksbill {Erodiwii) carpel. (4) Aristida sp. 



to prevent its ever being withdrawn, so that every 

 change of the twisting awn forces the sharp point down 

 into the skin ; and, as a matter of fact, sheep are killed 

 in this way. This species is found in Russia, but 

 strangely enough three other sheep-killing grasses are 

 known which act in precisely the same manner. One 

 Heteropogon contortus in New Caledonia, another Aristida 



