38 FIELD CROPS 



fruits, and is used more largely as the plant matures. All 

 the elements, however, are used more or less during the 

 entire growth of the plant. 



40. Result if an Element Is Lacking. If any one of the 

 important elements is lacking, continued healthy growth is 

 not possible. If nitrogen is wanting, the growth will be 

 slow and stunted and the plants will be j^ellow and sickty 

 in appearance. A shortage in the supply of potash often 

 produces weak, flabby plants which are likely to lodge. 

 Calcium seems to be necessary for the growth of leaves, and 

 iron for the development of the green coloring matter. 

 Phosphorus is more necessary for the production of seed than 

 for the growth of the stems and leaves, and plants will make 

 a larger growth if this element is lacking than if any other of 

 the important ones is not supplied. Potash apparently has 

 more or less influence on the formation of starch. Potash is 

 found most largely in the stems and leaves, and nitrogen and 

 phosphorus in the seeds of most plants. 



41. Necessities for the Growth of Plants, lo sum- 

 marize the j)receding paragraphs, plants require aii", sunlight, 

 water, heat and plant food in order to grow. Air is neces- 

 sary to supply carbon for the making of starch and for the 

 respiration of plants. Sunlight is required in the manufac- 

 ture of starch and other compounds, for plants can break 

 carbon dioxide into its parts only in the presence of sun- 

 light. Water is needed to combine with the carbon to makci 

 starch, to act as a carrier of plant food, to evaporate from thv, 

 leaf surfaces and keep the plant from getting too warm, and 

 to give rigidit}^ to the ciells of the plants. Heat must be 

 present in the optimum degree for the best germination. 

 Plant food is required to make the different compounds 

 which compose the plant. Soil is not necessary for the 

 growth of a plant, for many plants will mature in water if 

 their positions are constant and the necessaiy plant food is 

 supplied. Practicall}', however, soil is a necessity. 



