82 CARNEGIE INSTITUTION OF WASHINGTON. 



At present the failure to substitute for the cotyledons may be ex- 

 plained by one or more possibilities, among which are the following: 

 (1) that penetration of organic substances may be difficult; (2) that a 

 combination of various organic nutrients may be essential; or (3) that 

 the cotyledon contains an essential ''vitamine." 



Some Factors in the Salt Requirements of Plants, by B. M. Duggar. 



As a result of studies previously reported, the writer has drawn 

 attention to the necessity of taking into consideration the hydrogen- 

 ion concentration of the salt solution furnished such plants as wheat, 

 corn, and peas. When phosphate is furnished as the monobasic salt of 

 potassium, and when the other salts employed yield solutions which 

 are neutral or nearly so, the pH of the mixed salt solution may not be 

 far from the limit of acidity which the plants mentioned will tolerate 

 without experiencing a marked diminution in growth. Unfortunately, 

 the acid salts are not constant in pH unless carefully recrystallized, and 

 the variations encountered may be within either the optimal or supra- 

 optimal range. Moreover, the effects of conditions of growth must be 

 taken into consideration. It has been shown, for example, that high 

 temperature and low humidity (high evaporation) are directly or 

 indirectly related to increased acid injury. 



The favorable range of conditions for the growth of wheat afforded 

 by the climate of the Coastal Laboratory (Carmel, California) offered 

 an excellent opportunity to investigate further some of the factors 

 determining the maximum healthy growth of this plant. The usual 

 solution cultures were employed and all experiments were made with a 

 variety of wheat particularly suited to the conditions, namely, the 

 Pacific Bluestem, seeds of which were obtained from the Introduction 

 Garden of the U. S. Department of Agriculture at Chico, California. 

 The cultures were arranged in glass beakers exposed on a lattice table 

 in the open, and weighings of the plants were taken after a period of 

 28 days. Ten plants were included in each culture. 



In an important series completed during July and August 1919, 

 special attention has been directed to a determination of the most 

 favorable proportions of the salts in a solution consisting of potassium 

 nitrate, magnesium sulphate, calcium sulphate, and "soluble ferric 

 phosphate," previous work having indicated special merit in such a 

 combination of salts. In 21 cultures the compounds mentioned have 

 been variously combined in concentrations ranging from a minimum up 

 to four times this amount. In addition to varying the concentrations 

 of these salts, aluminium compounds have been added in certain cases 

 in the form either of aluminium hydroxide or postassium aluminium 

 silicate. In this particular group of cultures the range of hydrogen- 

 ion concentration has not been considerable, the maximum and 

 minimum pH values being 6.6 to 7.4. In all of these cultures there has 



