G YRA TION OF PLANTS. 167 



soil. The flower-heads are able to bury themselves in 

 garden mould or sand. The depth to which they pene- 

 trate, measured from the surface to the back of the head, 

 is from a quarter to half an inch. With plants in the 

 house a head partly buried itself in six hours. After 

 three days only the tips of the reflexed calices were 

 visible. In six days the whole had disappeared. Plants 

 growing out of doors are believed to bury their flower- 

 heads in a much shorter time. Only a few of the 

 flower-heads which from their position are not able 

 to reach the ground yield seeds, whereas the buried 

 ones never failed to produce as many seeds as there 

 had been perfect flowers. 



" It is unnecessary to enter into all the details of 

 observations on the movement of the footstalk, from 

 the time it begins to bend until the flower-head is 

 buried in the ground. Suffice it to say, that through- 

 out this period oscillation was going on. A peduncle 

 was watched during fifty-one hours, whilst in the act 

 of burying itself in a heap of sand. When buried 

 so that the tips of the sepals alone were visible, it 

 was rotating. When the flower-head had com- 

 pletely disappeared beneath the sand it was still 

 rotating. Any one who will observe this process 

 will be convinced that the rocking movement due to 

 the rotation of the peduncle bears an important part 

 in the act. Considering that the flower-heads are 

 very light, that the peduncles are long, thin, and 



