238 SCIENCE REMAKING THE WORLD 



ditions is the cause or result of the trouble. There arc 

 some indications that suggest a lack on these tubers of 

 a sufficient amount of an accessory growth-promoting 

 substance. It is possible by repeated sprouting to 

 cause normal tubers to produce typical spindling sprouts 

 even to the point when small tubers appear at the base 

 of the sprouts, a characteristic of severe cases of the 

 spindling sprout disease. Chemical analysis of the 

 mother tubers showed that very small amounts of the 

 usual food materials had been removed from the tubers 

 when the sprouts began to show decided spindliness 

 of growth. However, the tubers were exhausted of a 

 substance necessary for normal growth. 



In cool climates the spindling disease is rare, but it is 

 very prevalent in our southern states. Experimenta- 

 tion in recent years has proved conclusively the supe^ 

 riority of northern seed over home-grown seed for the 

 early crop in the more southern latitudes. The true 

 character of this place-effect in the production of seed 

 potatoes is certainly not definitely known, but it is be- 

 lieved that the spindling sprout disease is an important 

 contributing factor. 



During certain seasons the potato crop suffers much 

 damage by the premature death of the tips and margins 

 of the leaves, without evident parasitic causation. This 

 condition, known as tip-burn, has usually been attrib- 

 uted to the loss of water from the leaves by transpira- 

 tion at a more rapid rate than it can be supplied by the 

 roots under the prevailing climatic conditions. This 

 simple explanation of tip-burn has been recently con- 

 tested, and its true cause has truly become a real mod- 



