THE FUNCTION OF GREEN LEAVES. 49 



The seeds of grasses arc quite small, and should seldom be 

 covered more than the eighth or fourth of an inch deep. The 

 only need of a covering is to keep the seeds moist, and in some 

 cases to prevent birds or other small animals from eating them. 

 If planted deep, the supply of oxygen is liable to be insufficient, 

 or if it be present, the seed is likely to become exhausted or 

 much weakened in thrusting its young stem and leaves to the 

 surface, where it may reach the light and begin to make a per- 

 manent growth of green leaves. All exjjeriments are so much 

 modified by the weather and condition of the soil, that to give 

 definite rules is difficult. 



The Function of Green Leayes. — Leaves not unfrequently 

 absorb water in a liquid state as well as in the form of vapor, 

 yet the roots absorb most of the water for plant growth. That 

 leaves sometimes absorb water is most easily tested by observing 

 the revival of cut flowers or plants when placed in a moist, tin 

 box. 



" The paramount function of the leaf is the absorption and 

 assimilation of carbon, as such does not exist in the atmosphere, 

 unless, indeed, as an impurity in air of towns, and a very preju- 

 dicial one to plants." {Masters). The carbon of plants comes 

 from carbon dioxide, and is decomposed through the agency of 

 chlorophyll under the influence of light. 



Plants can endure darkness for a short time, but if long con* 

 tinued the chlorophyll disappears and the leaves fade, and 

 finally perish, as may be seen in warm weather where a board is 

 placed on the grass for some time. 



Unless the air is saturated with moisture, which is not com- 

 monly the case for long periods, the leaves evaporate large 

 quantities of water. The surplus passes ofP, leaving the con- 

 densed assimilated matter for building up the plant. In a grow- 

 ing season, while everything is thrifty, a grass-plant contains 

 70 to 80 per cent or more of water. 

 7 



