18 THE MODERN PEACH PRUNER. 



The embryo comprehends the radicle or rudi- 

 ment of the root, the plumule or rudiment of the 

 stem, and cotyledons, whose office it is to supply 

 nourishment to the young plant before the appear- 

 ance of the leaves. 



No. 3. — Phenomena connected with Growth. 



The substances necessary for the life of plants are 

 absorbed by them from the soil, by means of the 

 roots, and from the atmosphere, by means of the 

 leaves. De Jussieu calls these last " aerial roots." 

 Their functions, in some degree, resemble those of 

 the human lungs. They absorb from the air the 

 water and carbonic acid which they require. Roots 

 draw from the soil mineral and saline materials, 

 besides the carbon and nitrogen which artificial 

 manures supply. 



The spongioles alone are the absorbing organs 

 of the roots ; nutritive substances are introduced 

 by them in the form of liquids, which proves 

 how indispensable water is to vegetation. Fluid 

 nourishment is, therefore, the basis of the growth 

 of plants. It is elaborated in the leaves, under 

 the influence of the solar rays during the day. 

 Under the name of sap it ascends to the leaf- 

 stalks, passes into the venous ramifications, and 

 from thence into the cellular tissue of the leaf. 



