SECTIONAL TRANSACTIONS.—K. 489 
The behaviour of Vicia faba under parallel circumstances is very similar, except 
that, owing to the relatively large amount of nitrogen supplied by the seed, the eflects 
of early privation are somewhat delayed, and greater proportionate growth is made 
where nitrogen is entirely withheld. 
With both species tested, although the yield of dry matter is not increased by the 
provision of nitrogen during the later weeks of growth, the uptake of nitrogen continues, 
resulting in a progressively higher percentage content until the plants are approaching 
maturity. From experiments now in progress it will be possible to determine the 
distribution of this later absorbed nitrogen throughout the plant. 
Comparison of the response of barley to early and late supplies of nitrogen and 
phosphorus suggests that while the absorption of either element, if available, continues 
to a very late stage of growth, yet for the production of maximum yield nitrogen 
must be supplied for a longer period after germination than is necessary with 
phosphorus. 
On the other hand, though the supply of both elements during the first month or 
more of growth is essential for satisfactory ear production, the omission of phosphorus 
at this time causes more complete inhibition of ear formation than if nitrogen is 
withheld. It would appear, therefore, that barley can utilise supplies of nitrogen, 
after initial periods of starvation, more readily than it can respond to the provision 
of phosphorus under similar circumstances. 
Dr. BLopwen Lioyp.—Bacterial Denitrification. 
Bacterial denitrification is an oxidation-reduction process whereby nitrate is 
completely reduced to elementary nitrogen. The reduction takes place in three 
stages, from each of which oxygen is obtained by the reducing organism. The oxygen 
thus available is utilised for respiration. Nitrogen is liberated as waste metabolite 
only at the last stage. 
Dr. Cranston and Dr. Lloyd have found from their recent researches that by 
continuous measurements of the rate of gas production a ‘ denitrification curve ’ 
may be obtained for an actively denitrifying broth culture. Such a denitrification 
curve resembles in general a growth curve, but the two curves do not correspond 
exactly at the initial stages, for there is a * chemical lag ’ in addition to the ordinary 
bacterial lag. The total amount of nitrogen produced by a culture is a measure of 
the aggregate activities of the contained bacteria, and the rate of gas production at 
any given time is a measure of the number of active bacteria in a culture at that time. 
The following experimental conditions favour denitrification : low initial concentra- 
tion of nitrate (6 mg. per 10 c.c. of broth culture), high incubation temperature 
(37-40° C.), an alkaline reaction (pH 8-2), and little or no free oxygen. 
Dr. E. P. Smirx.—Calibration of Flower-colour Indicators. 
An attempt has been made to determine the pH value of the cell-sap of some 
coloured flowers by calibrating the anthocyanin pigments of the flowers. The pigment 
is extracted directly from the flower by heating the petals in samples of buffer mixtures 
of known pH values. In this way a series of colour-standards is obtained, showing 
the colour assumed by a particular flower-pigment over a chosen range. The short 
period of heating (5-10 seconds) gives a clear, brilliant extract which keeps its colour 
well, especially in the acid range. Four different buffer-mixtures were tested, of 
which the ‘ Universal Buffer Mixture’ of the British Drug Houses proved most 
satisfactory. (For further details of the method see Smith (2).) 
It was found that the flowers fell into three groups, as has been suggested by 
Buxton and Darbishire (I), namely, pure red, magenta (intermediate) and blue. The 
pure reds and blues can usually be assigned to their group by inspection, but not 
always (cf. Primula sinensis var. ‘ Etna,’ Viola cornuta). The reds were difficult to 
calibrate with the pH standards, because there were often two ranges of brown-red, 
about pH 6 and again about pH 9. Two cases were noted in which the anthocyanin 
was so concentrated in the cellsap that it was not ‘indicating’; these were the royal 
blue Cineraria and the very dark red Nicotiana, Sandev’s hybrid. 
The following flowers were studied :— 
