IV PLANT LIFE 37 



when these three requisites are present in proper proportions 

 the following process takes place : — The seed absorbs mois- 

 ture which causes all the parts to soften and swell so as to 

 burst the coverings and allow the embryo to grow ; at the 

 same time certain chemical changes are taking place, for The process 

 the insoluble starch or oil present in the seed is converted nafion"^'' 

 into a soluble substance like sugar upon which the miniature 

 plant feeds. The carbon let loose by this chemical change Chemical ac- 

 combines with the oxygen of the air to form carbonic acid. ''°" ^^^ "P" 

 During all these changes heat is given off, and thus the seed Heat 

 is supplied with warmth, to a certain extent, by its own vital 

 action, but outside heat is necessary in the first instance ; 

 for, without its presence, the life that is in the seed could 

 not be, as it were, wakened from its sleeping condition. 



The embryo having burst out of the coverings of the seed. The growth 

 the radicle pushes downwards into the soil to form the root, embryo. 

 and the plumule grows upwards to form the stem and leaves. 

 Nature has endowed the embryo with this property, and 

 nothing whatever can prevent the radicle from going down- 

 wards into the soil, and the plumule from growing upwards 

 into the air. If a seed be so planted as to have the radicle 

 directed upwards, it will turn downwards as soon as it com- 

 mences to grow, and the plumule will also turn round and 

 strike upwards— this may often be seen in the case of cacao 

 and other seeds which have been planted with the wrong 

 end upwards. 



The Nutrition of Plants. — It has been already seen 

 that the infant plant is suplied with food from the store of 

 nourishment kept for that purpose in the seed. But by the 

 time the roots and leaves are formed, this supply has been 

 eaten up, and the plant must now look to the soil and the 

 air for its food. The leaves absorb the nourishment from How plants 

 the air, and ihe roots take it up from the soil by reason of ^'^^'^• 

 the delicate hairs on their smallest fibres. In order that this 



