Chap. II. BREAKING THEOUGH THE GKOUND. 87 



root-stocks, &c., buried beneath the grotuid, the surface 

 is broken by a cone formed by the young imbricated 

 leaves, the combined growth of which gives them force 

 sufficient for the purpose. 



With germinating monocotyledonous seeds, of 

 which, however, we did not observe a large number, 

 the plumules, for instance, those of Asparagus and 

 Canna, are straight whilst breaking through the ground. 

 With the Gramineae, the sheath-like cotyledons are 

 likewise straight ; they, however, terminate in a sharp 

 crest, which is white and somewhat indurated ; and this 

 structure obviously facilitates their emergence from 

 the soil : the first true leaves escape from the sheath 

 through a slit beneath the chisel-like apex and at 

 right angles to it. In the case of the onion {Allium 

 oepa) we again meet with an arch ; the leaf-like coty- 

 ledon being abruptly bowed, when it breaks through 

 the ground, with the apex still enclosed within the 

 seed-coats. The crown of the arch, as previously 

 described, is developed into a white conical pro- 

 tuberance, which we may safely believe to be a 

 special adaptation for this office. 



The fact of so many organs of different kinds — 

 hypocotyls and epicotyls,.the petioles of some coty- 

 ledons and of some first leaves, the cotyledons of 

 the onion, the rachis of some ferns, and some flower- 

 stems — being all arched whilst they break through 

 the ground, shows how just are Dr. Haberlandt's * 

 remarks on the importance of the arch to seedling 

 plants. He attributes its chief importance to the 

 upper, young, and more tender parts of the hypocotyl 



' ' Die SehutzeinrichtunKen in tliough our observations lead U3 



der Eutwiokelung der Keim- to differ on some points from tho 



pflanze,' 1877. We have learned author, 

 much ilrom this interesting essay, 



5 



