IV.] 



GERMINATION. 



37 



slightly curved inwards, called the plumule j and, point- 

 ing downwards, the rudiment of the root, called the 

 radicle; the extremity of the radicle invariably nestles 

 immediately within the micropyle. The seed-leaves, or 



FIG. 28. One cotyledon of the Bean, showing the plumule and 

 radicle. 



cotyledons, of the Bean are opposite ; so we have an 

 embryo with a pair of cotyledons, or a dicotyledonous 

 embryo, 



1 6. If we put a few beans upon moist earth in a flower- 

 pot and cover them with a bell-glass, the first stage of 

 growth, termed germination, of the young Bean-plant 

 may be conveniently observed. The essentials to germi- 

 nation are found by experience to be a certain amount of 

 moisture, warmth, and air. If sufficiently warm (and the 

 amount of warmth required to commence with varies in 

 the seeds of different plants), moisture is absorbed by the 

 seed, which causes it to swell up so as to burst the seed- 

 skin. Oxygen, also, is absorbed from the air, and certain 

 chemical changes, accompanied with the liberation of 

 some carbonic acid, take place in the cells of the embryo, 

 resulting in the solid substances which they contain being 

 made available for the use of the growing plant. The 

 radicle is always the first to break out, curving down 

 towards the earth, whatever may be its position. The 

 radicle by its direct prolongation forms the primary root 

 of the plant. The plumule shortly after disengages itself, 

 ascends and develops into the stem of the Bean, bearing 

 foliage and flower-leaves. 



