THE DISPERSION OK SEbUS AN1> STORES. 117 



skewer which easily becomes entangled in the hairy- 

 covering of an animal. After a time, when the awn 

 dries and becomes brittle, the seed is detached and 

 falls to the soil. An aristate grain, on account of 

 its penetrating power, can avail itself of the move- 

 ments of any animal to which it clings, and so work 

 its way among the wool or hair vintil thoroughly, 

 entangled. The hygroscopic awns of Arena and 

 other gi"asses, which resemble Erodinvi in the power 

 which their seeds have of bur3'ing themselves, may 

 also act as prehensile organs. Farmers on the 

 pampas of South America have numbers of their 

 sheep killed annually by these burrowing grains 

 peneti'ating the hides and reaching the vital organs 

 of the animals. Centuries of cultivation have in all 

 probability so greatly altered the cereals that very 

 little can be inferred from their present condition 

 They are not now found in the wild state— a 

 circumstance which Hildebrand explains as due to 

 their having lost through cultivation their means of 

 dispersion, so that they are no longer able to hold 

 their own against natural species. Sevei'al members 

 of the order Gramineae, such as Poa, Ilolcus, Phalaris, 

 etc., are adapted to wind-dispersion where the 

 palese serve as wings. Hairy appendages occur in 

 Phragmites comviunis, Pennisetum villosuni, and 

 some others ; and Arena sterilis can disperse itself by 

 the assistance of its hygroscopic aw^i. These appear, 

 however, to be exceptional cases, and grasses in 

 general may be considered as having their seeds 

 adapted for dispersion through the agency of animals. 

 This, moreover, is only what we might expect when 

 we consider the vast herds of buffaloes, deer, 

 antelopes, and other large herbivores that still 

 inhabit the grassy plains of Africa, and till recently 

 roamed on the Asiatic steppes and American prairies. 

 Nature is economical of her means, and it is reason- 

 able to suppose that as an animal became dependent 

 on a certain class of plants for food, it should have 

 been utilised as an agent in their dispersion. In a 



