176 PLANT GROWTH 



The description of the relation of growth to nitrogen sup- 

 ply should be read in Chapter 14. It has been found that, 

 regardless of light, plants can build proteins in any actively 

 growing cell that has an adequate supply of carbohydrates 

 and nitrogen. Normally the nitrogen content of the soil 

 decreases during the summer, which causes a deficiency in 

 the plant resulting in carbohydrate storage. If a high ni- 

 trogenous fertilizer is applied in mid-summer or early fall the 

 plants may respond with a rapid growth which will not 

 harden or mature enough to avoid winter-killing. 



The root systems of plants with high nitrogen are smaller 

 in proportion to the tops when compared with those from 

 better-balanced nitrogen-level plants (Plate XIII). For 

 this reason high nitrogen plants will suffer more quickly from 

 drought. A simple experiment to study the root effect of 

 nitrogen may be made by using plants in pots and treating 

 with varying amounts of nitrogen as described above. A 

 garden experiment would be better if the removal of the 

 roots is not too great a task. 



A study of the influence of growth and storage of carbo- 

 hydrates may be made by keeping a high nitrogen level with 

 roses by heavy pruning through the summer or by adding 

 nitrogen to the soil at frequent intervals. Normally high 

 nitrogen will stimulate excessive new growth until late fall. 

 The new growth will not be hardened resulting in more 

 winter-killing, and the following summer the growth may be 

 poorer because of the lack of stored food. 



Nitrogen is commonly applied as nitrate of soda or as 

 ammonium sulphate. The sodium leaves a more alkaline 

 medium and the sulphur a more acid one. Acid-loving plants 

 should have the latter, but if it is used on other plants it will 

 be necessary to use lime more frequently. Ammonium 

 nitrate may be used, in which case the nitrogen is available 

 from both the acid and alkaline radicle. The nitrogen cycle 

 diagram shows that plants are able to use either the am- 



