INFLUENCE OF HYBRIDIZATION AND CROSS-POLLINA- 

 TION ON THE WATER REQUIREMENT OF PLANTS 



By Lyman J. Briggs, Biophysicist in Charge, Biophysical Investigations, and H. L. 

 Shantz, Plant Physiologist, Alkali and Drought Resistant Plant Investigations, 

 Bureau of Plant Industry 



INTRODUCTION 



In breeding plants for drought resistance it is desirable to know 

 whether the water requirement of the hybrid progeny bears a definite 

 relationship to the water requirement of its parents. That hybridization 

 may result in increased drought resistance is indicated by the work of 

 Collins/ who observed that certain first-generation hybrids of maize 

 suffered less from drought than the parents grown under the same con- 

 ditions. The behavior of these hybrids suggests that they may be 

 exceptionally efficient in the use of water, a point of practical importance 

 in connection with drought resistance. This consideration, combined 

 with the fact that water-requirement measurements constitute a physio- 

 logical expression of the elTects of hybridization, led the writers to measure 

 the water requirement of a number of hybrids and their parents, the 

 subject being one which has not heretofore been quantitatively investi- 

 gated. These measurements, which were conducted at Akron, Colo., 

 were made possible through the courtesy of Mr. G. N. Collins, of the 

 Ofiice of Crop Acclimatization and Adaptation Investigations, Bureau of 

 Plant Industry, who supplied seed of a number of first-generation hybrids 

 of maize and their parent strains. Mr. J. H. Parker, of the Office of 

 Cereal Investigations, Bureau of Plant Industry, also kindly furnished 

 seed of a hybrid strain of wheat and its parent strains. 



The term "water requirement" is here used to designate the ratio of 

 the total weight of water absorbed by the plant during its growth to the 

 total dry matter produced, excluding the roots. The plants were 

 grown in large iron pots of a type already described.^ To exclude rain- 

 fall and prevent evaporation from the soil as far as possible, each pot 

 was provided with a tight-fitting cover having openings for the plants, 

 the annular space between the stalk and the cover being closed with a 

 plastic wax. The plants made a normal growth, as reference to Plate 

 LVIII will show. 



> Collins, G. N. The value of first-generation hybrids in com. U. S. Dept. Agr. Bur. Plant Indus. Bui. 



191. p. 32- I9I0- 



2 Briggs, L. J., and Shantz, H. L. The water requirement of plants. I.— Investigations in the Great 

 Plains in 1910 and 191 1. U. S. Dept. Agr. Bur. Plant Indus. Bui. 284, p. 9. 1913- 



Jotimal of Agricultural Research, Vol. IV, No. s 



Dept. of Agriculture, Washington, D. C. Aug. 16, 1915 



G — 52 



(391) 



