IV.] 



ERODIUM. 



heat. Now if the awn were fixed instead of the seed, 



it is obvious that during the process of untwisting, the 



seed itself would be pressed downwards, and, as M. 



Roux has shown, this mechanism thus serves actually 



to bury the seed. His observations were made on an 



allied species, Erodium cincoium, which he chose on 



account of its size. He found that j, 



if a seed of this plant is laid on the 



ground, it remains quiet as long as it 



is dry ; but as soon as it is moistened i 



— i.e. as soon as the earth becomes I 



in a condition to permit growth — I 



the outer side of the awn contracts, 



and the hairs surrounding the seed 



commence to move outwards, the 



result of which is gradually to raise 



the seed into an upright position with 



its point on the soil. The awn then 



commences to unroll and consequently 



to elongate itself upwards, and he 



suggests that as it is covered with 



reversed hairs, it will probably press 



against some blade of grass or other 



obstacle, which will prevent its moving 



up, and will therefore tend to drive ''■"^it^S'" 



the seed into the ground. If then (Aft=r Sw=ee.) 



the air becomes drier, the awn will again roll up, 



in which action M. Roux thought it would tend to 



draw up the seed, but from the position of the hairs 



the feathery awn can easily slip downwards, and 



would therefore not affect the seed. When moistened 



once more, it would again force the seed further 



I 



/ 



