DISSEMINATION OF SEEDS. 133 



contract into narrow spiral coils, causing the cone to turn 

 on its axis and to penetrate the ground, and the erect 

 hairs on it which point upwards retain it there like 

 grappling-hooks. After the cone has penetrated the 

 ground, the twisted part of the awn does the same, driv- 

 ing the part which contains the seed further and further 

 into the soil. If the mericarp now becomes moistened, 

 the coiled part attempts to straighten itself but its coils 

 are held by the hairs which stand on the convex surface ; 

 and this movement also contributes to drive the cone 

 deeper into the soil. Whether therefore the moisture is 

 greater or less, the mechanical contrivance produces the 

 same effect, namely, to drive the part of the mericarp 

 which contains the seed into the soil." 



The twisted awn of Avena fatua, or wild oats, and of 

 some other plants, seems to have been specially intended 

 to aid the further dispersion of the seed on being dis- 

 charged from the plant. This spiral awn or spring which 

 is beset with a multitude of tine, minute hairs possesses 

 the property of contraction by drought and of expansion 

 by moisture ; hence it remains in a perpetual state of con- 

 traction and dilatation dependent on the weather. From 

 these changes in the length of the awn, as well as from 

 the additional aid of the hue hairs which act as so many 

 fulcra and cling to whatever object they meet, the seed to 

 which it is attached remains in motion until it germinates 

 or is destroyed. When the seeds of oats are ripe, it is 

 said that they are projected with such violence that in a 

 dry day one may hear them thrown out with a slight, 

 sudden snap. 



Darwin experimented with the seeds of Stipa pennata, 

 feather grass, and reached conclusions nearly identical 

 with the preceding. 



