2 Feeds and Feeding. 



great quantities of water from the soil, giving most of it off again 

 to the air thru its leaves and green parts. Lawes and Gilbert of 

 England found that wheat and clover plants take from the soil by 

 their roots and give to the air thru their leaves about 200 Ibs. of 

 water for each Ib. of dry matter they produce. 



Next to water, carbon dioxid or carbonic acid gas is the great 

 food material of plants. Ten thousand parts of air contain about 

 4 parts of carbon dioxid, and about 28 tons of this gas rests over 

 each acre of the earth's surface. The supply of carbon dioxid is 

 never exhausted from the air because thru the decay and dissolu- 

 tion of plant and animal matter it is being constantly returned 

 thereto. On the under surface of plant leaves are innumerable mi- 

 nute openings or pores, leading inward among the cells of the leaf 

 structure. The air, penetrating these pores, supplies carbon dioxid 

 which is absorbed into the cells and thus enters the plant proper. 



Nitrogen abounds in the living, growing parts of plants. Despite 

 the fact that about three-fourths of the air is nitrogen gas, with the 

 exception noted farther on, plants cannot take it up as such, but 

 obtain their supply from the soil by means of their roots, either in 

 the form of nitrates or as ammonia, chiefly the former. 



The mineral substances required by plants are taken from the 

 soil thru the roots. They may be grouped as follows : 



Sulfates 



Phosphates 



Nitrates 



Chlorids 



Silicates 



Carbonates 



potassium. 



calcium. 



magnesium. 



iron. 



sodium. 



ammonium. 



Sulfur, in small amount, is a component of plant proteins. Phos- 

 phorus, likewise in small amount, is present in the life-holding pro- 

 toplasmic protein of the leaf cells and also abounds in the protein 

 of seeds. Potassium, vital to the formation of plant protoplasm, 

 is probably one of its components. Iron also seems to have a spe- 

 cific function to perform in the growth of the plant. It is univer- 

 sally found in plant tissues. Calcium and magnesium are vital to 

 plants, tho their uses are not well understood. Silicon and sodium, 

 tho always present, are regarded by some authorities as not essen- 

 tial to plant life. 



Free oxygen gas is absorbed by seeds during germination, and a 

 small amount is being constantly absorbed by the leaves and fruits 

 of plants. Bacteria inhabiting nodular growths on the roots of 



