234 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
relation was noted between the concentration on" opposite sides and the rate 
of water movement through the membrane. — R. J. L. 
Permeability of Membranes as Related to their Composition. By F. E. 
Denny (Bot. Gaz. vol. Ixiii. No. 6, June 1917, pp. 468-485; 6 figs.). — The 
investigations described in this paper were carried out in order to discover what 
substances in the membrane determine the rate at which water can pass through 
it. Quantitative measurements showed lipoids, tannins, and pectic substances 
to be factors in determining the permeability of membranes to water. 
Suberized layers were not found to be significant in the membranes studied, 
and the presence of soluble proteins could not be detected. — R. J. L. 
Peroxidases, The Mode of Action of Plant. By G. B. Reed (Bot. Gaz. vol. 
lxii. Sept. 1916 ; 2 figs.). — In a previous paper by the same author on the 
" Mechanism of Oxidase Action," he has shown that colloidal platinum charged 
at sufficiently frequent intervals with oxygen will bring about the oxidation of 
various substances at a rate approximating that affected by hydrogen peroxide 
and colloidal platinum. From this he concluded that " the action of the colloidal 
metal in accelerating oxidation by hydrogen peroxide (that is, its peroxidase 
action) is due to the taking of oxygen from the peroxide by the metal to form a 
compound which is a more efficient oxidizing agent than the original peroxide." 
From these investigations the author has passed to an analogous investiga- 
tion of the more significant and complicated problem of the nature of peroxidases 
produced in living tissue, as it seemed probable that the mechanism of the 
reactions must be similar. 
As the result of experiments conducted first with the active ferment of 
horseradish root, and later with potato peroxidase, the processes were shown to 
be essentially the same. It is concluded therefore that in oxidation processes 
catalysed by peroxidases two reactions are involved. Firstly, the peroxidase 
combines with oxygen from the oxygenases (or from some other source) to form 
an intermediate compound which is a more energetic oxidizing agent than the 
original source of the oxygen ; secondly, the oxidation is then affected by this 
intermediate compound. — R. J. L. 
Phosphates contained in Mineral Phosphates, The Nature of. By G. S. 
Robertson (Jour. Agr. Sci. vol. viii. Part 1 ; Sept. 1916). — Various mineral 
phosphates were finely ground and extracted with 2 per cent, solution of citric 
acid. The ratio of the phosphoric pentoxide to the calcic oxide in the extract 
point to formulae of the type mCa 3 P 2 0 8 , wCaO. Florida Island phosphate, for 
example, is represented by m = 4, n = 3. If the mineral phosphate be calcined 
before extraction, a citric acid soluble silica phosphate is formed, together with 
one or more phosphates with a lower lime content than the original phosphate. 
/. E. W. E. H. 
Phosphates, Manufacture of Acid. By W. H. Waggaman (U.S.A. Dep. Agr., 
Bur. Soils, Bull. 144, December 1914). — A description of the manufacture of 
acid phosphate ; the various processes are well described, and there are some good 
illustrations of the various types of machinery used. — C. P. C. 
Phosphoric Acid and Potash : The Production and Fertilizer Value of Citric 
Soluble. By W. H. Waggaman (U.S.A., Dep. Agr., Bur. Soils, Bull. 143, Nov. 
1914). — Phosphate rock and felspar are mixed together with a small quantity 
of iron and manganese to assist fluidity, and heated for twenty minutes to 
1400 0 C. ; the resulting product is a fertilizing material containing both phosphate 
and potash. It not only shows high solubility in citric acid solutions, but is 
fairly good in water saturated with carbon dioxide. 
Pot tests gave good results, although not so high as those obtained by the 
use of acid phosphate and sulphate of potash, but quite sufficient to indicate 
a high fertilizing value. — C. P. C. 
Phosphorus Compounds of the Soil, The Relation between Dilute Acids and 
the. By E. J. Russell and J. A. Prescott (Jour. Agr. Sci. vol. viii. Part 1, 
Sept. 1916). — It was Daubeny, in 1845, who first used the terms " active " and 
" dormant " to distinguish soil constituents soluble in dilute acid from those not 
soluble. Dyer, in 1894, suggested the use of one per cent, citric acid solution 
to distinguish active and dormant plant food. In Sweden 2 per cent. HC1 is 
used, in Germany a saturated solution of carbonic acid, while aspartic, acetic, 
and other acids have also been employed. Hall and Amos, Sigmund, and the 
present authors have at different times in the last ten years endeavoured to 
ascertain what happens exactly to phosphates contained in soil when the soil 
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