Volume 4, Issue 2
August 1936, pages 67-177
pp 67-74 August 1936
During decomposition of glucose byAzotobacter chroococcum there is no evidence to suggest that the immediate products of fermentation of the sugar are used up in nitrogen fixation. The major part of the fixation takes place even while the sugar is present in the medium.
The water soluble products left after the complete disappearance of sugar, when inoculated with fresh culture of Azotobacter do not fix any nitrogen.
From these and other evidence, it has been concluded that the mechanism of fixation of nitrogen in the soil is different from that by Azotobacter alone.
In the early stages of sugar decomposition by Azotobacter correspondingly more of carbon is fixed in the slime and bacterial cells than nitrogen, the C-N ratio of the cells and slime being very high. Later on the ratio adjusts itself to the initial level. There is close correlation between growth of the organism and nitrogen fixation.
pp 75-91 August 1936
pp 92-96 August 1936
pp 97-107 August 1936
pp 108-121 August 1936
pp 122-127 August 1936
The incomplete reduction of nitrate (over 50 parts per million) in the chromo-sulphuric acid digest by zinc is traceable to the presence of the mercury salt in the digesting mixture. The mercury forms a coat of hydride around unattacked zinc and thus prevents further action with acid.
The interference of mercury can be eliminated and accurate estimates of nitrates in soils (upto 300 parts per million) obtained by adding extraquantity of sodium sulphite to the digest until a black precipitate is obtained. The suspension is then raised to boil and treated with zinc in the usual way.
The efficiency of zinc in reducing nitrate in the digest is traceable to the joint action of chromium and sulphite. On treatment of acid with zinc the latter forms hydrogen sulphide which is directly responsible for the removal of small quantities of nitrous acid that may be formed during reduction. The mechanism of the related processes has been discussed.
The commoner samples of reduced iron contain ferrous sulphide, so that the non-formation of nitrous acid during reduction of nitrate by that reagent is traceable to hydrogen sulphide. The ferrous salt present in solution behaves in a manner similar to the chromium salt and thus prevents loss of nitrogen during reduction.
pp 128-138 August 1936
Alisma plantago L.—The pollen grains are three-nucleate with two malecells. As reported by Dahlgren (1928) the development of the embryo sac is of the ‘Scilla-type’, but besides the usual six-nucleate embryo sacs, sevennucleate embryo sacs have also been seen and there is a probability that in rare cases eight-nucleate embryo sacs also occur.
Alisma plantago-aquatica L.—Stages in microsporogenesis and development of the male gametophyte do not show any features of special interest. The development of the embryo sac corresponds to that ofAlisma plantago (Dahlgren, 1928), but seven- or eight-nucleate embryo sacs are also formed occasionally. The endosperm is free nuclear.
Sagittaria graminea Mich.—Six-nucleate embryo sacs are the rule, but some were found to have seven nuclei. One or both the synergids sometimes assume an egg-like appearance and develop into embryos. More than one pollen tube may enter the embryo sac. The endosperm is of the ‘Helobialestype’ and the embryo follows the same course of development as described forS. sagittifolia (Souèges, 1931).
pp 139-162 August 1936
pp 163-170 August 1936
When fairly large quantities of mixed calcium salts of organic acids (obtained after anærobic fermentation of sugar) are added to a mineral medium containing soil, only a small portion of the added organic matter is used up in the course of 12 days. The quantity of nitrogen fixed, though small, is proportionately high when compared with the carbon utilised.
When the acid products are added directly to the mineral medium, (without neutralisation) there is fairly rapid utilisation of carbon. There is also correspondingly greater fixation of nitrogen.
When varying quantities of acid products are added together with the sugar, the best return of nitrogen for the carbon utilised is obtained when the mixed calcium salts are of the order of 20 mg. of the organic carbon to 10 g. of the soil.
When the mixed calcium salts are added after the sugar is completely used up, there is enhanced fixation of nitrogen, the ratio of fixed nitrogen to the carbon utilised being as 1: 20.
Trials with two different types of soil (one, a red sandy loam, and the other, an alkali soil) showed that the mixed calcium salts are used nearly to the same extent in both the cases. The corresponding fixation is also similar, yielding ratios ranging between 1: 13 and 1: 17.
The significance of the foregoing observations and their possible extension to field practice are discussed.
pp 171-177 August 1936
Highly active preparations of inulinase can be obtained from a species ofaspergillus which is grown on artichoke nutrient media. Comparative culture experiments have revealed that phosphates definitely stimulate the formation and enrich the inulinase content of the preparations.
The fungus preparation can be preserved for months in a dry and active condition after treatment of the crop with anhydrous acetone. The inulinase can be extracted from this powder by maceration with toluene saturated water at room temperature, and stable extracts are thus obtained which maintain their enzymic activity unimpaired for months.
It has been found that a definite relationship exists between the phosphorus content of the preparation and their inulinase activity both in the case of the powders and their maceration extracts, while the total and amino nitrogens of the extract bear no relation with its enzyme activity.