106 SCIENTIFIC AGRICULTURE. 



STRUCTURE AND FUNCTIONS OF THE ROOT. 



The internal structure of the root and stem are similar : the 

 fibrils are composed of vascular tissue, inclosed in a cellular 

 epidermis, which, however, does not extend to the ends of the 

 fibrils; these ends are naked and spongy, hence they are 

 called spongioles, and have the power of absorbing large quan- 

 tities of water. 



The growth of the root takes place by layers upon its 

 surface and the addition of matter at the extremities. The 

 fact is considered established, [Johnston,] that the spuigioles 

 absorb gaseous as well as aqueous matters, when in contact 

 with them. The root absorbs only from its spongioles ;-> from 

 these it is carried by the vessels of the fibrils to those of the 

 main roots, and thence into the stem and to all parts of the 

 plant. 1. Both organic and inorganic substances, in a state of 

 solution in water, enter the circulation of plants. 2. The roots 

 have the power of selecting such substances as are necessary 

 for their food, and of rejecting those that are^njurious to their 

 healthy growth. 3. Roots possess the power of excreting 

 certain matters which are in excess, or are unnecessary or 

 injurious to them. 4. Roots have the power of modifying the 

 fluids as they pass through them. [Johnston.] 



THE STALK OR STEM. 



The part of a plant which rises above the surface of the 

 soil, which constitutes the principal axis, and is intermediate 

 between the roots and branches, is called the stem. The 

 direction of the stem is generally vertical, but in some plants 

 it is oblique or horizontal. Stems, like roots, may be annual, 

 biennial or perennial. Plants are divided into kerbs, shrubs, 

 and trees, according to the size and duration of the stem. 



Herbs are plants with annual roots and annual stems, which 

 do not become woody: such are the grasses, mints, most 

 flowers, <&e. 



Shrubs have perennial, woody stems and roots, divided into 



