Permeability 133 
indicating alternating periods of absorption and excretion. This was 
observed for example in Vida Faba in potassium bromide, sodium 
monohydrogen phosphate, calcium nitrate and barium nitrate; 
Valonia utricularis in ammonium sulphate, magnesium sulphate, 
potassium dihydrogen phosphate, ammonium nitrate or potassium 
bromide; yeast in zinc sulphate or calcium chloride. But as the method 
of Pantanelli involves the use of different plant material for each 
analysis, it seems possible that the differences recorded resulted from 
differences in the absorbing capacity of the various batches of plants 
used. Pantanelli is aware of this difficulty, but thinks that as a 
source of error it is negligible because he had four plants in every 
vessel and took care to use plants having equal development both of 
root and shoot. 
I think it is likely Pantanelli has underrated the magnitude of 
variation possible among plants that appear very similar to the 
eye. Miss Redfern (1922 a) performed similar experiments on the 
absorption of calcium and chlorine ions from solutions of calcium 
chloride by living plants of Pisum sativum and Zea Mays. Careful 
selection of plants that appeared equally developed was made at the 
commencement of the experiment, each plant was g' own singly in 
water culture and for any determination of absorption separate 
analyses were made of the solutions in which six plants had been 
growing. From these results it was possible to calculate the probable 
error of the determination of absorption, and although owing to the 
small number of plants no great exactitude could be claimed for the 
results, yet these brought out very plainly the great variations that 
may occur in absorption by apparently exactly similar plants. The 
results also showed that within the limits of probable error there 
was no indication of such a periodicity in absorption as that recorded 
in a number of cases by Pantanelli, absorption proceeding con¬ 
tinuously to an equilibrium value attained in the case of peas after 
about 24 hours, and in the case of maize after about 48 hours. 
Subsequent excretion of the salt appears to be due to the approach 
of death of the plant. Further work with other plants is necessary, 
however, before it can be denied with certainty that the apparent 
oscillations observed by Pantanelli can be definitely explained as 
due to differences between individual plants. 
