4 CIRCULAR NO. 116, BUREAU OF PLANT INDUSTRY. 



THE SCIENCE OF CROP PHYSIOLOGY. 



The problem of securing the most productive crop plant is by no 

 means as simple as most of our agricultural experts have assumed. 

 We are all aware that the plant breeder can modify any existing 

 variety and breed into it new qualities or breed out of it undesirable 

 qualities. There has been rather too much of a disposition to accept 

 this power of modifying varieties like a gift of manna from Heaven 

 and to assume that mere selection and simple breeding are all that is 

 needed to bring our crop plants up to the maximum of efficiency. 

 Nothing could be farther from the truth. 



Three centuries of botanical exploration carried out in the interest 

 of science by self-sacrificing men, often working under the greatest 

 difficulties, have revealed the existence of thousands, yes, tens of 

 thousands of plants either directly useful to man or closely related 

 to species already in use. - 



Any really intelligent and effective attempt to breed superior va- 

 rieties of crop plants must be preceded by a botanical survey of the 

 related wild material with a view to securing the best possible forms 

 to work with in attempting such amelioration. If a crop plant shows 

 some marked deficiency, some obvious inability to adapt itself to the 

 climatic and soil conditions of the regions where its culture is at- 

 tempted, the earth should be scoured for related types of plants which 

 can be used to supply the deficiency. Resistance to cold, to heat, to 

 drought, to insect and fungous enemies, or to a hundred and one un- 

 favorable climatic conditions can often be secured by hybridizing our 

 crop plants with skillfully chosen wild forms and then systematically 

 improving the hybrid offspring by modern methods of plant breeding. 



The most efficient improvement of our crop plants and the most 

 effective utilization of the wild types for this improvement necessi- 

 tates a knowledge of the climatic and soil requirements of the crop 

 plants themselves. Increased knowledge of such facts often leads 

 to unexpected results. For instance, many of the sorghums are well 

 known to be more drought resistant than Indian corn. However, a 

 study of the life historj^ of sorghums reveals the fact that the zero 

 point of growth of the .voung seedling is relatively very high and in 

 consequence sorghum can not be planted as early in spring as corn, 

 but must be sown in most parts of the West a month or more later. 

 This sometimes causes the young sorghum to be exposed to severe 

 drought before it is old enough and has sufficient depth of root to be 

 able to withstand such exposure. In other words, it is probable that 

 the drought resistance of sorghum may be materially increased by 

 securing races of sorghum which through being native to northern 

 latitudes or through centuries of culture in cold regions have acquired 

 the power of germination at low temperatures. A lowering of the 



[Cir. 116] 



