100 CIKCUMNUTATING MOVEMENTS OF CHAP. II. 



cotyl, with the two legs fixed in the ground, certainly 

 circumnutates, and as it consists of a single internode, 

 we may conclude that it grows in the manner de- 

 scribed by Wiesner. It may be added, that the crown 

 of the arch does not grow, or grows very slowly, for 

 it does not increase much in breadth, whilst the arch 

 itself increases greatly in height. 



The circumnutating movements of arched hypo- 

 cotyls and epicotyls can hardly fail to aid them in 

 breaking through the ground, if this be damp and 

 soft; though no doubt their emergence depends 

 mainly on the force exerted by their longitudinal 

 growth. Although the arch circumnutates only to a 

 slight extent and probably with little force, yet it is 

 able to move the soil near the surface, though it may 

 not be able to do so at a moderate depth. A pot with 

 seeds of Solanum paUnacanthum, the tall arched hypo- 

 cptyls of which had emerged and were growing rather 

 slowly, was covered with fine argillaceous sand kept 

 damp, and this at first closely surrounded the bases of 

 the arches ; but soon a narrow open crack was formed 

 round each of them, which could be accounted for 

 only by their having pushed away the sand on all 

 sides ; for no such cracks surrounded some little sticks 

 and pins which had been driven into the sand. It 

 has already been stated that the cotyledons of Phalaris 

 and Avena, the plumules of Asparagus and the hypo- 

 cotyls of Brassica, were likewise able to displace the 

 same kind of sand, either whilst simply circumnu- 

 tating or whilst bending towards a lateral light. 



As long as an arched hypocotyl or epicotyl remains 

 buried beneath the ground, the two legs cannot sepa- 

 rate from one another, except to a slight extent from 

 the yielding of the soil; but as soon as the arch 

 rises above the ground, or at an earlier period if 



