80 THE MECHANICAL FUNCTIONS. 



Of the functions of spongioles in absorbing fluids 

 I shall have occasion to speak when treating of 

 nutrition. But as the roots exercise a mechan- 

 ical as well as a nutrient office, we should here 

 consider them in the light of organs adapted 

 to procure to the plant a permanent attachment 

 to the soil, upon which it is wholly dependent 

 for its supply of nourishment. It is scarcely 

 necessary to point out how effectually they per- 

 form this office. Our admiration cannot fail to 

 be excited when we contemplate the manner in 

 which a large tree is chained to the earth by its 

 powerful and widely spreading roots. By the 

 firm hold which they take of the ground, they 

 procure the most effectual resistance to the force 

 of the winds, which, acting upon so large a 

 surface as that presented by the branches 

 covered with dense foliage, must possess an 

 immense mechanical power. 



The principal seat of the vitality of a plant is 

 the part which intervenes between the root and 

 the stem. Injuries to this part are always fatal 

 to the life of the plant. 



As the roots penetrate downwards into the 

 earth to different distances in order to procure 

 the requisite nourishment, so the stem grows 

 upwards for the purpose of obtaining for the 

 leaves and flowers an ample supply of air, and 

 the influence of a brighter light, both of which 

 are of the highest importance to the maintenance 



