. Carnegie Institution of Washington publication. ACIDITY DETERMINATIONS. 35 decrease was maintained up to 60 hours, after which a slight rise was to be noticed. This last-named circumstance may very well be due to the fact that after 1\ days the wound periderm had formed sufficiently to protect the cut surfaces. The subsequent experiments with wound respiration bear out this probability. The acidity of a parallel specimen, which had not been wounded, shows the ordinary slight decrease in acidity which comes as a result of long- continued darkness. It may be inferred that this diminution of ac
. Carnegie Institution of Washington publication. ACIDITY DETERMINATIONS. 35 decrease was maintained up to 60 hours, after which a slight rise was to be noticed. This last-named circumstance may very well be due to the fact that after 1\ days the wound periderm had formed sufficiently to protect the cut surfaces. The subsequent experiments with wound respiration bear out this probability. The acidity of a parallel specimen, which had not been wounded, shows the ordinary slight decrease in acidity which comes as a result of long- continued darkness. It may be inferred that this diminution of acid is largely the effect of the increased exposure to the oxygen of the air consequent on the injury. MISCELLANEOUS. In tests made to determine the region of highest acidity it was found that the cortex is usually more acid than the pith, while leaves are of about the same acidity as the outer layers. Young fruits did not show the increased amount of acid that might be expected, though they do perhaps contain somewhat more acid than the ordinary tissues. It did not appear that the acidity varied to any noticeable extent in different parts of any one joint. A long, young joint showed at the base a similar acidity to that at the tip. Similarly, none of the mature joints that were tested showed any indication of inequalities in the longitudinal distribution of the acids. 3AM. I2m'd't. 3AM. 6AM iSnoort. FIG. 4.—Graph showing acidity of Mammillaria grahami in comparison with diurnal temperature curve. The acidity is given in terms of of decinormal alkali per gram fresh weight. = acidity. = temperature. Attention has already been called in the chapter on experimental methods to the differences of acidity in shoots of unequal ages. The young growing joints are distinctly more acid, on the average, than the mature ones, both as to the total amount present and as to the concentration of the juice. Shoots of the age of 1 or 2 years are hardly separable on the basis of
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