GERMINATION OF A SEED 19 



maintenance of the life and the nutrition of the 

 protoplast. 



As the plant gets older and larger a considerable 

 amount of differentiation of its internal substance 

 becomes necessary. This we shall study later. Mean- 

 time we may say that these changes are accompanied 

 by the death of some of the protoplasts. The mem- 

 branes or skeleton of these protoplasts are left in the 

 interior and subserve certain important purposes ; but 

 the protoplasts remain in full vigour towards the 

 exterior and particularly towards the extremities of 

 both shoots and roots, where new formation of them is 

 continually taking place. 



The living substance is thus situated in greatest 

 amount towards the outside of the plant and at its 

 extremities, where its contact with the environment can 

 be most easily maintained. The subordinate mechanisms 

 of its life, which are concerned with its mechanical sup- 

 port and with the efficient working of its body and the 

 co-ordination of its various forces, are hidden away more 

 deeply in its interior. 



CHAPTER II 



THE EARLY DEVELOPMENT OF A PLANT THE GERMINA- 

 TION OF A DICOTYLEDONOUS SEED 



THERE is a great variety in degree of development 

 among the plants which exist upon the earth. The 

 most highly organised of these are the so-called flowering 

 plants, to which most of the terrestrial forms belong. 



These plants have a certain feature in common which 

 distinguishes them from all others. They form seeds, 

 which become separated from the parent and after a 

 period of rest develop into new plants. A seed is essen- 

 tially a very young plant in a dormant or resting 



