168 The Potato 



very difficult to use any cultivator or ridging tool late in 

 the season without cutting these lateral roots. The loss 

 of root area is further increased by the loss of the vertical 

 roots attached to these lateral ones. 



The relation of the value of these roots to the yield of 

 the crop is vital. One function of the roots of the growing 

 plants is to take in water containing plant-food in solution. 

 The water is transpired from the leaves and the plant- 

 food transformed into material for further growth of the 

 plant. Transpiration from the leaves of the potato is less 

 easily checked in periods of drought than with many other 

 plants. The potato has less ability to regulate its use of 

 water by the supply available. Removing part of the 

 leaves by pruning or by attacks of disease reduces the yield 

 by taking away from the plant the factory in which the 

 material for the tubers is elaborated. As the supply of 

 water and plant-food remains the same, such pruning may 

 even be of benefit in the cases where the normal food 

 supply is deficient. The removal of part of the roots not 

 only removes a fraction of the supply of water and food, 

 but, from the nature of the plant, throws it out of balance. 

 The leaves continue to transpire water, and in the lack of 

 full supply from the root, use up part of the water in the 

 plant itself. The whole plant suffers, the greatest injury 

 showing at the tips of the leaves. The ends of the leaves 

 dry up and die, a trouble commonly called "tip-burn." 



The strain upon the potato from exliausting effects of 

 blossoming and forming tubers at nearly the same time is 

 very heavy. The heat and drought which often occur at 

 this time add to the troubles of the plants. Any damage 

 to the plant is now more dangerous than before. At this 

 time, tillage may be beneficial or may be very injurious. 

 If the weather is cool and the soil water ample, tillage may 



