Atkins — The Hydrogen Ion Concentration of Plant Cells. 417 



indicator, and of specially prepared indicator papers. "Wagner (1916) 

 previously employed the drop method, using lacmosol as indicator in work 

 on plant immunity. Indicator papers were also used by Hempel (1917) in a 

 research on succulent plants. 



Felton (1921) has found this drop method very serviceable for work on 

 tissue cultures, and thinks it preferable to working with 2-3 mm. tribes and 

 diluted liquid, owing to dilution errors in fluids of low buffer action. It was 

 also tried by Jameson and Atkins (1921) for work on the tissues of the silk- 

 worm, and has been used by the writer for a year with, it is thought, fairly 

 reliable results. 



Determinations of hydrogen ion concentrations in 2:ilant tissues. 



When working upon the hydrogen ion changes taking place in the course 

 of the mahai or fermentation of indigo, it seemed desirable to see what 

 relation the final st^ge (which was at about pH 5-6, as far as could be judged in 

 the brownish liquid of a small-scale fermentation) bore to the acidity of the 

 indigo leaf. It may be remarked that the initial value was about pH 8'5, 

 i.e., that of the river-water. The plan adopted was to crush portions of 

 indigo leaf on white porcelain, with the addition of one or two drops of 

 distilled water, and to compare the colours given with methyl red and 

 brom cresol purple against those which appeared with the standard buffer 

 solutions. It is always advisable to use two indicators where possible, as it 

 lessens the chance of any serious error. In this way it was found that the 

 leaves of young and old plants were of acidity pH 5'6, whereas cotyledons still 

 in the seed-coat were slightly less acid, pH 5'8. Determinations were thus 

 made upon various Indian plants, and are recorded elsewhere (Atkins 1921). 

 In addition to working with crushed tissues, an attempt was made to use the 

 indicator on sections in order to see whether adjacent cells differed noticeably 

 in acidity, for it seemed possible that in crushing a stem the result might 

 give a very misleading idea of the true condition of the conducting tracts. 



For example, it was found that varieties of the castor-oil plant (liicinus 

 communis), grown at Pusa, gave pH 4-6 for the stem, for both red- and 

 green-stemmed plants, but the tissues were not examined separately. 

 It was similarly found that young leaves, older leaves, and a young flower 

 were at pH 4-8. A section across the seed-capsule with very immature 

 seeds showed, however, that the wall tissues were at pH 4-8, while the seeds 

 were much less acid, pH 5'4. Had the capsule been crushed, an erroneous 

 result would have been obtained. The acidity of the crushed pollen sacs 

 was also pH 5-4, as nearly as could be judged. 



SOIENT. PROC. R.D.S., VOL. XVI, NO. XXXI. 3 A 



