414 PHYSIOLOGY [Bot. Absts. 



2829. McLean, R. C. Studies in the ecology of tropical-rain forest; with special reference 

 to the forests of south Brazil. I. Humidity. Jour. Ecology 7: 5-54. / pi., 21 fig. 1919. 



MINERAL NUTRIENTS 



2830. Buckner, G. Davis. The composition of the ash of crab grass (Digitaria sanguin- 

 alis) as affected by the soil in which it is grown. Jour. Amer. Chem. Soc. 41 : 1384-1385. 1919.— 

 The author, while searching for a green plant which contained a large percentage of ash, no- 

 ticed that crab grass (Digitaria sanguinalis) grew and flourished in the middle of a limestone 

 roadway. Comparative analyses were made of a plant grown under the above conditions and 

 of a sample of the same species grown under normal conditions in garden soil. Due care was 

 taken in selecting and preparing the samples. The analyses showed that the intake of in- 

 organic material was not the same in the two specimens, i.e., the sample grown in a compara- 

 tively new limestone roadbed which was from 4-5 inches in thickness contained approximately 

 16 per cent less ash than did a similar sample grown in garden soil. The K2O was 18.8 per cent 

 less in the first mentioned sample. The sample grown in the limestone contained 22.7 per 

 cent more P2O6, 44.0 per cent more CaO and 27.6 per cent MgO. The amount of silica in the 

 two samples was approximately the same. "The outstanding feature in connection with the 

 growth of these two samples of crab grass is that the absorption and retention of these differ- 

 ent amounts of calcium, magnesium, phosphorus and potassium cause no observable differ- 

 ence in their external appearance." — J. M. Brannon. 



2831. Krishnamurti Row, K. The effect of salinity on the growth and composition of 

 sugarcane varieties. Agric. Jour. India 14:476-493. 11 pi. 1919. — See Bot. Absts. 3, Entry 

 2928. 



2832. Volhard, J. [Rev. of: Ehrenberg, Paul, and Otto Nolte. Der Einfluss von 

 der Pflanze aufgenommener Manganmengen auf ihre Zusammensetzung. (Influence of ab- 

 sorbed manganese on plant composition.) Landw. Versuchsst. 90: 139-145. 1917.] Bieder- 

 mann's Zentralbl. Agrikulturchem. 47: 334-335. 1918. — The reviewer reports that with the 

 use of manganese the authors obtained oat straw which analyzed 0.03 per cent to 0.10 per cent 

 of manganese. The grain contained 0.0035 to 0.02 per cent of manganese. When the man- 

 ganese content was 0.0139 per cent the ash was 11.0 per cent while with a content of 0.0939 

 per cent manganese the ash was 12.2 per cent. It was thus shown that an increase of the man- 

 ganese content of plants to 0.1 per cent produces no certain appreciable changes in the com- 

 position of the incombustible matter of the plants. — F. M. Schertz. 



• 

 PHOTOSYNTHESIS 



2833. Long, Frances Louise. The quantitative determination of photosynthetic activity 

 in plants. Physiol. Res. 2: 277-300. 1919. — The method here tested depends on the determ- 

 ination, by means of Fehling's solution, of the reducing power of an aqueous extract of the 

 tissues to be studied. The preparation of the extract and the technique of the chemical de- 

 termination are the main considerations. Similar lots of material (as leaves) are gathered 

 at the beginning and end of an experiment-period and the extracts prepared from these are 

 compared with respect to their reducing powers. The difference in reducing power (calcu- 

 lated) as amount of dextrose per unit of material employed) is taken to be a measure of the 

 total net photosynthetic activity of the tissues in question, for the experiment-period. — To 

 prepare the aqueous extract, the (fresh or dried) material is first finely subdivided and boiled 

 in water, to extract water-soluble substances from the insoluble portion and to gelatinize 

 starch. After cooling, the mass is digested with "Taka" diastase. The boiling and digest- 

 ing process is repeated three times and the material is then boiled a fourth time, after which 

 it is treated with lead acetate and excess of this reagent is precipitated with sodium carbonate. 

 The solid material is then filtered out. The extract thus obtained is next boiled with dilute 

 HC1, and NaOH is finally added to render it only slightly acid. To the resulting extract 



