RESPONSE OF CITRUS SEEDLINGS IN WATER CUL- 

 TURES TO SALTS AND ORGANIC EXTRACTS 



By J. F. Breazealu 



Associate Biochemist, Office of Biophysical Investigations, Bureau of Plant Industry, 

 United States Department of Agriculture 



INTRODUCTION 



This paper deals with the growth of citrus seedUngs in water cultures 

 and their reaction to various salts and to organic matter in solution. 

 The experiments were conducted mainly at Riverside, Calif., in connec- 

 tion with other investigations relating to the causes of the malnutrition 

 of citrus trees. Lemon, grapefruit, and several varieties of orange seed- 

 lings (Blood, Tahiti, Mission, Valencia, Tangerine) were used in the ex- 

 periments; but the work was confined largely to grapefruit and lemon 

 on account of the relative ease with which the seeds could be secured. 



EXPERIMENTAL METHOD 



The seeds were sprouted in trays of coarse sand about lo cm. deep 

 and were covered to a depth of about i cm. At ordinary spring and 

 summer temperatures it requires about 30 days to develop citrus seed- 

 lings to a stage suitable for culture work, but under greenhouse condi- 

 tions this time can be reduced to about 20 days. The germination 

 period of the grapefruit and lemon is somewhat less than that of the 

 orange. The seeds should not be given much water during the geraii- 

 nating period. The citrus seedling is hardy and will stand drouth. Hot 

 sunshine is likely to scald the primary leaves, so it is advisable to keep 

 the seedlings in half shade. 



When the seedlings were large enough to be used, the sand around the 

 roots was saturated with water and the seedlings were withdrawn from 

 the seed bed. The sand was washed off and the roots dipped into a thick 

 paste of carbon black to a depth of about i cm. The carbon black 

 sticks to the radicle and forms a well-defined index, so that the subse- 

 quent elongation of the root tip can be accurately measured. Five to 

 10 seedlings bound together lightly with a small piece of absorbent cotton 

 were usually placed in each culture flask. Of the citrus seedlings so far 

 tested, the lemon is by far the most satisfactory for use in water cul- 

 tures, for the radicle is straight and the cotyledons do not separate as in 

 the grapefruit. 



It was found that the citrus seedling is especially sensitive to the toxic 

 substances in distilled water. A treatment with carbon black that would 



Journal of Agricultural Research, A'^ol. XVIII, No. s 



Washington. D. C. Dec. i, 19.9 



su Key No. G-180 



(267) 



