28o FREAKS OF PLANT LIFE. 



familiar to all who have observed the members of the 

 family. That the twisting is the result of an hygro- 

 metric property in the awn has been demonstrated by 

 Professor Asa Gray.^ He says : "The narrow carpel is 

 pointed at the base ; the long awn or style in drying 

 bends at right angles with the carpel, and twists in 

 many turns, depending on the amount of dryness, 

 and untwists in a moister air or when wet. We had 

 wondered that no one seemed to have given an 

 account of the way in which this mechanism acts so 

 as to bury the seed in the ground. Dispersed by the 

 wind over the loose or sandy soil which these species 

 prefer, the seed bearing end, being the heavier, lies 

 next to the ground, and is the comparatively fixed 

 point around which the long awn makes circular 

 sweeps, whether in twisting or untwisting. This 

 gives a rotary movement to the carpel, fixes the sharp 

 end in the soil, and, whether twisting or untwisting, 

 causes it to bore into and bury itself in the ground." 

 M. Roux says that in Erodhnn, when the seeds are 

 thus interred, the moisture of the soil soon destroys 

 the epidermis, and this allows the long beak to de- 

 tach itself at its articulation with the style, leaving it 

 planted in good condition quietly to germinate. 

 Thus then, it may be seen that, by their own hygro- 



' " Use of Hygrometric Twisting of the Tail to the Carpels of 

 Erodium," " Ainerican Journal," 3rd series, vol. xi., 1879, p. 153. 



