THE FUNDAMENTALS OF CROP IMPROVEMENT. 5 



zero point of growth of the young seedling might easily have a pro- 

 found effect on the drought resistance of sorghum as a crop. 



Here we can see the distinction between crop physiology and plant 

 physiology. Crop physiology is the application of the principles 

 of plant physiology to the production of crops in a profitable and 

 efficient manner. The plant physiologist who is studying drought 

 resistance would be very little interested in the temperature require- 

 ments for germination of the plants he is working with. The crop 

 physiologist, on the other hand, who is attempting to discover 

 methods of growing a profitable crop in dry regions might find it 

 a matter of the utmost importance to investigate these thermal rela- 

 tions which at first thought seem to have no bearing on the problem 

 at hand. This study of plant-life history or crop physiology gives 

 a point of view which, when carried over into botanical exploration, 

 enables us to select with more discriminating judgment those wild 

 types of plants best adapted for use in improving our cultivated 

 crops. 



A NEW BRANCH OF ECONOMIC BOTANY. 



This brings us to the point where we can appreciate the need of 

 developing a new branch of botanical study of the morphological 

 and physiological characters of the wild plants related to our culti- 

 vated crops with a view to determining their relationships and their 

 availability for use in the improvement of our crop plants. Many of 

 our agricultural investigators think of botany as a science of plant 

 names or laboratory experiments with little or nothing in the way 

 of practical relations to agricultural problems, but for the most effi- 

 cient improvement in crop plants we must look to this new branch 

 of botany for a thorough survey of the wild relatives of our culti- 

 vated plants. The crop physiologist must investigate the life history 

 not only of the crop plant itself but of its wild relatives before he 

 can begin to understand the possibilities of applying botanical science 

 to agricultural problems. 



The necessity of a knowledge of this new economic botany and 

 crop physiology for the proper improvement of crop plants is strik- 

 ingly shown in the work of breeding hardy citrus fruits. The first 

 attempt along this line was the crossing of our common orange with 

 the hardy deciduous Citrus trifoliata of Japan and China. When in 

 a dormant condition Citrus trifoliata can withstand intense cold- 

 temperatures of 10° or even 20° F. below zero do not affect it — 

 but the fruit is small, very seedy, contains scarcely any juice, and the 

 skin is full of intensely acrid oil. In spite of these drawbacks the 

 first-generation hybrids with the orange have turned out to be of 

 considerable value and constitute a new race of hardy citrus fruits, 



[Cir. 116] 



