CELL-NUCLEUS FERTILISATION 247 



of the ovule the embryo begins to develop. 

 Gradually the ovule changes into the seed. 

 Reserve materials of food accumulate within 

 it, and are most frequently stored either 

 in the growing endosperm, or partly (seldom 

 wholly) in the sporangium wall (nucellus, 

 perisperm). If the embryo reaches any con- 

 siderable size within the seed, it may presently 

 destroy these tissues, and absorb the nutritive 

 contents into its own body. When this 

 happens, some part of the young plantlet 

 usually becomes thickened and so forms the 

 repository for the food. Most commonly it 

 is the seed leaves (cotyledons), as in the 

 bean, or it may be the young stem below 

 them, as in the brazil-nut, which thus becomes 

 charged with the reserves of food. 



In whatever way the food material is dis- 

 posed, however, it is always so situated as to 

 be readily available when the young plantlet 

 starts into growth, on the germination of the 

 seed. 



It does not invariably happen that con- 

 siderable stores of food after this fashion 

 await the embryo on its awakening to its 

 new life. Many of the flowering plants have 

 followed other lines than that of transmitting 

 to a relatively small posterity large accumula- 

 tions of hereditary capital. The commonest 

 alternative is seen in the production of vast 

 quantities of small seeds. The seed and the 

 contained embryo have been well cared for 

 during the earlier stages but they are cast 



