J 06 HUPTUEE OF THE SEED-COATS. Chap. IL 



allowed to germinate in damp air, and now a thin 

 flat disc was developed all round the base of the 

 hypocotyl and grew to an extraordinary breadth, like 

 the frill described under Mimosa, but somewhat broader. 

 Flahault says that with Mirabilis, a member of the 

 same family with Abronia, a heel or collar is developed 

 all round the base of the liypocotyl, but more on one 

 side than on the other ; and that it frees the coty- 

 ledons from their seed-coats. We observed only old 

 seeds, and these were ruptured by the absorption of 

 moisture, independently of any aid from the heel and 

 before the protrusion of the radicle ; but it does not 

 follow from our experience that fresh and tough fruits 

 would behave in a like manner. 



In concluding this section of the present chapter it 

 may be convenient to summarise, under the form of an 

 illustration, the usual movements of the hypocotyls 

 and epicotyls of seedlings, whilst breaking through the 

 ground and immediately afterwards. We may suppose 

 a man to be thrown down on his hands and knees, and 

 at the same time to one side, by a load of hay falling 

 on him. He would first endeavour to get his arched 

 back upright, wriggling at the same time in all 

 directions to free himself a little from the surrounding 

 pressure ; and this may represent the combined effects 

 of apogeotropism and circumnutation, when a seed is so 

 buried that the arched hypocotyl or epicotyl protrudes 

 at first in a horizontal or inclined plane. The man, 

 still wriggling, would then raise his arched back as 

 high as he could ; and this may represent the growth 

 and continued circumnutation of an arched hypocotyl 

 or epicotyl, before it has reached the surface of the 

 ground. As soon as the man felt himself at all free, he 

 would raise the upper part of his body, whilst still on 



