514 W. Wendler: Chemische Physiologie 1923—1924 [22 
269. Pfeiffer, Th. Die Möglichkeit eines teilweisen Ersatzes 
der Phosphorsäure durch Kieselsäure in den Pflanzen. (Mitt. d. 
Landw. Ges. Berlin 1923, p. 196—198.) 
270. Popp, M. Die Bedeutung einer Magnesiadüngung für 
unsere Kulturpflanzen. (Angew. Botanik 5, 1923, p. 20—21.) 
271. Pratt, C. A. The staling of fungal eultures. I. General 
and chemical investigation of staling by Fusarium. (Ann. of Bot. 
38, 1924, p. 563—595, 1 Fig. im Text.) 
272. Prianischnikov, D.N. Zur physiologischen Charakteristik 
von Ammoniumnitrat. (Journ. f. Landw. Wissensch., Moskau 1, 1924, 
p. 22—28. Russisch mit deutscher Zusammenfassung.) — Ref. in Bot. Ctrbl., 
N.F.5, 1925, p. 340. 
273. Prianischnikov, D.N. Nitrate und Ammoniaksalze als Stick- 
stoffquellen für höhere Pflanzen. (Zeitschr. Russ. Bot. Ges. 8, 1923 
[1924], p. 5—14. Russisch mit deutscher Zusammenfassung.) — Ref. in Bot. 
Ctrbl., N. F. 7, 1926, p. 13—14. 
274. Prianischnikov, D.N. Sur l’assimilation de l’’ammoniaque 
par les plantes superieures. (Rev. gen. de Bot. 36, 1924, p. 5—11.) — 
Ref. in Bot. Ctrbl., N. F. 5, 1925, p. 339— 340. 
275. Prianischnikov, D.N. Das Verhalten von Pflanzen und 
Tieren gegen Ammoniak. (Journ. f. Landw. Wissensch., Moskau 1, 1924, 
p. 179—190, 9 Tab. im Text. Russisch mit deutscher Zusammenfassung.) — 
Ref. in Bot. Ctrbl., N. F. 5, 1925, p. 339. 
276. Raybaud, L. Sur la flore microscopique de l’acide citrique 
a diverses concentrations. (C. R. Soc. Biol. 88, 1923, p. 803—805.) — 
Ref. in Bot. Ctrbl., N. F. 3, 1924, p. 138. 
277. Rayner, M. C. The vascular plants characteristic of peat. 
A criticism. (New Phytolog. 23, 1924, p. 2883—292.) — Ref. in Bot. Ctrbl., 
N.F. 6, 1925, p. 339—340. 
278. Reed, H. S. and Haas, A.R.C. Nutrient and Toxic Effects 
of certain Ions on Citrus and Walnut Trees with especial Refe- 
rence to the Concentration and pp of the Medium. (Univ. Calif. 
Publ. Agricult. Exp. Stat. of the College of Agriculture Technical Paper, Nr. 17, 
1094, 9. In, 28 Mie,) 
279. Reed, H. S. and Haas, A.R.C. The effect of hydroxyl-ion 
ceoncentration on the growth of walnut roots. (Amer. Journ. Bot. 
11, 1924, p. 78—84, mit 4 Textfig.) — ‚Preliminary experiments have shown 
that walnut seedlings may be successfully grown for a time in water cultures, 
and that they are very sensitive to the absence of calcium from the eulture 
solution. Seedlingss may be grown for some time in a solution of a single 
ealecium salt, but perish quickly when kept in a culture solution containing 
all the necessary nutrients except caleium. When the roots are alternately 
supplied with a caleium hydrate solution and with a calecium-free solution 
for 24-hour periods, marked injury is evident during the second exposure 
to the calcium-free solution. Walnut seedlings have been grown successfully 
for periods of at least a week in solutions of calecium hydrate (pp 9,0 or some- 
what higher) which were renewed continuously during the entire period. It 
seems logical to conclude, therefore, that the injury to walnut roots from 
solutions of high pp values is to be ascribed prineipally to caleium starvation 
ratber than to the effect of high concentration of hydroxyl ions upon the plant.“ 
