94 PLANT GROWTH 



of the tissues (due to lack of stored food), and smaller root 

 growth. 



Kraus and Kraybill in 1918 used tomato plants in a study 

 of the carbohydrate to nitrogen ratio. Although their clearly 

 described results greatly clarified this problem, which has 

 received much attention, there are still some unexplained 

 angles. They divided the carbohydrate to nitrogen ratio in 

 a way so that four conditions or results were obtained with 

 the plants: (1) A very high carbohydrate to nitrogen ratio, 

 where nitrogen, being very greatly limited, probably limits 

 growth with a resultant weakly vegetative plant condition. 

 (2) A high carbohydrate to nitrogen ratio, where nitrogen is 

 available but carbohydrates are in excess and occur in stor- 

 age form, results in heavy fruiting. (3 ) A low carbohydrate 

 to nitrogen ratio in which both are abundant but no carbo- 

 hydrate is in excess for storage, results in high vegetative 

 growth. (4) A very low carbohydrate to nitrogen ratio, in 

 which the plant appears to be starved for carbohydrate, 

 results in weakly vegetative growth. 



The balance of root and shoot or the ratio of carbohy- 

 drate to nitrogen may be varied in any one of a number of 

 ways. Pruning of the root or shoot is commonly practiced. 

 Removing some of the shoot reduces the leaf surface and the 

 carbohydrate supply from photosynthesis, which tends to 

 lower the ratio if the nitrogen supply remains the same and 

 for the healthy plant should result in number three con- 

 dition. This is essentially the result obtained by pruning 

 roses as is indicated by the size of new growth compared with 

 a rose that is not pruned, but pruning must not be so severe 

 that the number of flowers is reduced below a desirable set. 

 Heavy applications of nitrogen may get the balance so abnor- 

 mal that few flowers are produced because so little carbo- 

 hydrate food is stored. 



Root pruning will result in a decrease in the root absorb- 

 ing surface and the supply of nitrogen. This tends to in- 



