CROP PRODUCTION 159 



in its several growth phases in widely different manners. The 

 nutrient element required today may not be liberated until tomorrow ; 

 and the stimulations making for increased growth and reproduction 

 one day, may under apparently the same conditions lead to decreased 

 production. Investigations on the rots of corn which are being con- 

 ducted in this state are attracting the attention of corn growers every- 

 where. Two examples from this work will give additional proof as 

 to how plant physiology lies at the very foundation of such studies. 



Researches conducted by James G. Dickson, at the University of 

 Wisconsin, point to a relatively high optimum temperature for the 

 growth and sporulation of wheat scab and corn rot organisms, Gib- 

 berella saubinetii. When this fungus is inoculated on to corn and 

 wheat seedlings, the maximum development occurs at widely different 

 temperatures. On wheat growing under greenhouse conditions, the 

 fungus behaves as we would normally expect it to ; its growth is most 

 rapid and the greatest injury is caused to the host when the tempera- 

 ture is high. When grown on corn, practically the reverse is true. 

 The greatest growth of fungus and the least growth of the young corn 

 plants takes place under relatively low temperature environment. This 

 would suggest the desirability of planting corn late in the season when 

 the temperature is high. However, some Illinois experiments with 

 diseased corn show that when corn planting is delayed the severity of 

 the disease is increased, the yield reduced, and the quality of grain 

 lowered. Thus it is manifest that two organisms that have similar 

 optimum temperature requirements when grown alone, may have 

 widely different requirements for their best growth when one is 

 allowed to parasitize the other. Also when any one of the controlled 

 standard conditions is changed, the relationship of the host and parasite 

 is affected. In other words, there seems to exist in nature a state of 

 equilibrium between plants and the various factors which make up 

 their environment. When any one or more of these are altered, the 

 others are affected and the equilibrium is changed accordingly. 



Further, our corn-rot investigations bring sharply to mind the 

 problem of disease resistance and immunity. One instance will suffice 

 to bring this point clearly before us. We have two lots of corn, one 

 lot very much like the other, and when planted on clean land the 

 yields are about the same, but when planted on infested land the yield 

 of one was reduced about fifty-two per cent and the other only about 

 two per cent. Why this great difference? We naturally ask our- 

 selves, What is disease resistance and what is immunity to disease? 



Such problems are typical of studies in the physiological behavior 

 of different kinds of strains or varieties of corn, and upon such studies 



