26 



FIELD CROPS 



and peas should be planted deeper than clover and grass seed; 

 less care is also required in the preparation of the seed bed. 

 Veiy fine seeds, like tobacco, may best be sown by sprink- 

 ling them on the surface of a verj^ fine seed bed and pressing 



the seeds into the earth 

 with a board. 



Too much water is 

 undesirable, for it not 

 onlj^ excludes the air 

 from the soil but 

 causes the seed to rot. 

 On the other hand, a 

 dr}^ soil does not con- 

 tain moisture enough 

 so that the seed can 

 take up enough to start 

 or develop the neces- 

 saiy growth. The right 

 kind of seed bed is a 

 fine, moist, mellow one 

 — which does not drj^ 

 out readily and yet 



Figure 6.— A poorly drained field. Good drain- alloWS plentV of air tO 

 age, permitting the air to penetrate the sou, '^ ^ ^ 



is an essential condition for the germination rcacll SprOUtiuS! SCeds. 

 of seed and the growth of plants. ^ ^ 



WHAT THE LEAVES DO 



23. Assimilation. The leaves are the laboratory, or the 

 workroom, of the plant. Three important processes are 

 carried on in this workroom. These are assimilation, res- 

 piration, and transpiration. By assimilation, the tissues 

 of the plant are ]:)uilt up. The carbon dioxide of the air 

 is taken in through the leaf membranes and combined with 

 water to make starch. This process takes place only in the 

 presence of sunlight and only in the green parts of the plant. 

 The green coloring matter (chlorophyll) is of importance to 



