6 THE STORY OF PLANT LIFE 



which is on a different plan to that of the pea or the 

 mustard. 



The end of the main axis of the embryo opposite 

 the radicle is pointed in the grain of wheat. It appears 

 outside the grain shortly after the radicle and grows 

 straight upwards. The first leaf-structure has no 

 blade. The first true leaf has both a sheath, which 

 almost encases the stem, and a blade which gradually 

 unfolds and assumes a position more or less vertical. 



It will be seen that the above account includes 

 three types of germination. It is possible to distin- 

 guish a fourth. In the mustard there is no endo- 

 sperm, but many dicotyledonous seeds with endosperm 

 have epigeal cotyledons. 



The germination of the pea and mustard may be 

 taken as typical of Dicotyledons, that of wheat as 

 typical of Monocotyledons. There are numerous 

 details in which individual species do not conform 

 to types, so that the study of germination gives a 

 wide field for observation. 



At a still later stage in most cases it is possible to 

 make out that the radicle has developed into a root 

 with a main axis and a root-tip, and above this are 

 root-hairs for absorption. 



Rootlets are also given off at an angle with the 

 main root. In Leguminous plants root-tubercles 

 with bacteroids are soon developed. 



At the opposite extremity the shoot has a main 

 axis or stem. This bears leaves. In the axils are 

 buds, which in turn give rise to branches. The 



