SUMMARY OF PLANT NEEDS 39 



require a specially liberal supply of nitrogen. Phosphorus, 

 on the other hand, is an important constituent of seeds and 

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

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

 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 yellow and sickly 

 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 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. To sum- 

 marize the preceding paragraphs, plants require air, 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 dioxid into its parts only in the presence of sun- 

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

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

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

 to give rigidity to the cells of the plant. Plant food is 

 required to make the different compounds which compose the 

 plant. Soil is not necessary for the growth of a plant, for 



