488 SECTIONAL TRANSACTIONS.—K. 
dioxide relations of the tissue, stirring, surface-volume relations of the tissue, external 
salt concentration, &c.) and permitted accurate estimation of the carbon-dioxide 
produced by the tissue. This involved several novel features especially designed 
for this investigation. Maximum absorption was obtained under those conditions 
which produced maximum aérobic respiration, and this was secured by using a rapid, 
controlled stream of gas of known composition for aération. A preliminary survey 
of the variables affecting absorption of potassium bromide by potato suggested that 
this accumulation is determined by the metabolic activities of the living cell. The 
oxygen partial pressure in the aérating gas stream by determining the respiration rate 
and, therefore, the energy available to the system, also determined the salt absorption. 
The relationship between respiration and salt absorption was also evident when the 
behaviour of similar discs of varying thickness were studied. It was found that a 
thin surface layer of immersed discs of potato tissue respired much more actively 
than the central core. Moreover, it was apparent that these cells of highest respiration 
rate attained the highest salt content. These observations could be correlated also 
with certain anatomical and cytological changes which occur in the surface cells. 
The form of the absorption-time curves seems to indicate that previous curves supposed 
to indicate the attainment of a physico-chemical equilibrium are really due to the 
neglect of the oxygen-carbon-dioxide variable. Data obtained simultaneously for 
salt absorption and respired carbon-dioxide revealed certain difficulties in the way 
of interpreting salt absorption as a direct interchange of HCO, ions for absorbed anions 
+ 
and H ions for absorbed cations. It appears probable that anions and cations may 
be absorbed in stoichiometrically equivalent amounts. The potassium bromide 
absorbed appeared in the readily expressed sap, could be recovered quantitatively, 
and caused the expected increase of electrical conductivity of the sap. Apparently 
it existed in true solution in the vacuole. These facts are in accordance with the 
idea that the living cell does work, the source of energy being a metabolic one, not 
only in effecting absorption but in maintaining existing concentration gradients, and 
are not in accordance with an adsorption or other equilibrium mechanism. 
Dr. W. H. Pearsaty.—Temperature Effects in Plant Metabolism. 
The transformations of material taking place in plant tissues kept at different 
temperatures have been studied, in collaboration with Miss M. Pilling. The tissues 
used consisted of leaves kept at temperatures between 0° and 26° C. for periods of 
from thirty to fifty hours, and also of apples stored for more prolonged periods. 
Insoluble materials tend to be hydrolysed at low temperatures below 5° C. as well 
as at higher temperatures above 15° C. These changes have apparently not been 
recognised previously for proteins or nitrogenous constituents. They occur when 
carbohydrates are present in excess and their existence throws considerable light on 
certain current problems. 
Dr. Wintrrep E. Brencatey.—The Value of Nitrogen at Different Periods 
of Plant Growth. 
The value of nutrient elements, as nitrogen, phosphorus and potassium, varies 
throughout the lifetime of the plant, and their presence or absence is more critical 
at some stages of development than others. With barley, grown in water culture, 
the absence of nitrogen during the earlier stages causes rapid decrease in general 
growth and in ear development. If nitrogen is withheld for several weeks at this 
time the plants tiller freely, though ear formation is inhibited, but if starvation is 
very prolonged tiller production ceases and a travesty of an ear is produced at the 
expense of the nitrogen stored in the grain, little response being made to later supplies 
of the element. 
The reverse process, i.e. withdrawal of supplies after an initial period in the presence 
of nitrogen, is less disadvantageous. Normal ears are produced even when nitrogen 
is given only for the first month, and if it is present for the first eight or ten weeks 
the plants develop well and produce plenty of ears, which ripen off in good time. 
Longer periods of presentation tend to encourage increase in height up to a certain 
limit, but eventually maximum yield is reached, and later supplies of nitrogen have 
no beneficial effect, tending rather to delay ripening and render the plant more 
susceptible to disease attacks. 
