216 COMPOUND ORGANS OF TLANTS. 



Fig. 111. 



Fig. 111. Vertical section of the campulitropous seed of the red campion (Lychnis,) 

 showing the curved embryo. 



1. The radicle. — This constitutes the lower extremity of the 

 embryo, which in developing forms the root, or which gives birth 

 to it. It appears very often under the form of a little round or 

 conical teat. This, by germination, sometimes elongates and 

 becomes the body of the root. Its extremity continues naked 

 and afterwards divides. This mode of development, which is 

 characteristic of Phanerogamous plants having two seed-lobes or 

 cotyledons, is termed exorhizal, {l^a outwards, and l^^a a root.) 

 At other times the radicle in germinating, after having taken 

 a certain degree of elongation, stops the teat at its extremity, 

 becomes covered with a cellular layer as with a sheath, through 

 which breaks forth one or more fibres, which constitute the 

 true roots of the embryo. This kind of development, which 

 is peculiar to such phanerogamous plants as have only one seed- 

 lobe, is termed endorhizal, CMov within,) and the sheath formed 

 at the extremity of the radicle teat is called the coleorhiza, 

 [xo'Kio; a sheath, and jji^a a root. Fig. 112, shows both kinds 

 of germination. 



The plumule forms with the radicle the axis of the embryo. 

 It is developed after the radicle, which it surmounts, and with 

 which it is united. It exists only in Dicotyledonous embryos, 

 and is terminated at its summit by the gemmule. It is the 

 plumule which, by its development, produces the stem. It 

 commences from the point where the cotyledons are attached 



