118 FOREST BOTANY AND FORESTRY [BoT. Absts., Vol. VII, 



806. Morel, C. Activite de I'assimilation chlorophyllienne chez le pin sylvestre, quantite 

 d'eau necessaire a la vegetation d'une foret de cette essence. [Activity of chlorophyll assimi- 

 lation and water requirements of Scotch pine.] Rev. Eaux et Forets 58: 163-166. 1920. — 

 Dry wood contains about 50 per cent carbon, and air about 0.3 per cent carbon dioxide. 

 For a forest of Scotch pine to produce 5 cubic meters of wood per hectare per year, it is there- 

 fore necessary for the chlorophyll in the leaves to come into contact with 7,715,000 cubic 

 meters of air. This means that during the 1,200 hours of insolation in the period of vegeta- 

 tive activity between May 1 and September 1, the leaves must absorb every second a volume 

 of air equal to nearly one-fifth of their own volume; or, in other words, that the openings in 

 the chlorophyll tissues must fill and empty themselves of air at least every two seconds. The 

 pine leaf is thus far from being an inert organ. Assuming that each cubic meter of air expired 

 contains on the average 20 grams of water vapor, which is certainly a maximum, the leaves 

 would transpire each year 154,000 kilograms of water per hectare. Assuming further that 

 evaporation from the leaves and other parts of the tree is twice the transpiration, the total 

 annual water requirement of the forest is approximately 500,000 kilograms per hectare. This 

 is equivalent to a water blanket over the surface of the soil 5 centimeters in depth. In spite 

 of so small a water requirement, Scotch pine forests sometimes fail to produce a normal amount 

 of wood because they are in general relegated to soils which do not retain capillary water well, 

 because the humus which they produce improves only slightly the physical properties of the 

 soil, because the root hairs occupy a comparatively thin layer of soil, and because the tree 

 itself has but little reserve capacity. While Scotch pine seldom dies of drought, a soil which 

 is desiccated during the growing season may thus result in reduced wood production. Condi- 

 tions may be considerably improved bv underplanting open stands with such species as beech 

 or hornbeam, which produce a heavy leaf litter. — S. T. Dana. 



807. MoRviLLEZ, F. L'appareil liberoligneux foliaire des Betulacees, Corylacees et 

 Castaneacees. [The vascular anatomy of the leaves of the Betulaceae, Corylaceae, and Casta- 

 neaceae.] Compt. Rend. Acad. Sci. Paris 170:674-677. 12 fig. 1920.— See Bot. Absts. 6, 

 Entry 1903. 



808. Oechslin, M. FelssturzimBannwald Altdorf (Uri). [Rock avalanche in the forest 

 of Baun, Altdorf.] Schweiz. Zeitschr. Forstw. 71 : 150-154. 1 pi. 1920.— On January 4, 

 1920, a slide occurred near Moos Lake at an elevation of about 1050 m. The slide started at 

 one point and divided into two paths through the forest. Strips 150 to 200 m. wide were 

 torn out, and all of the timber and rocks were piled at the base. Approximately 10 ha. 

 (about 25 acres) of forest were completely destroyed, including about 2,000 cubic m. of tim- 

 ber, three-fourths of which was buried among the debris. The slide occurred on a 35° to 40° 

 slope. Slides in this region are caused by the porous condition of the soil and rock at the 

 surface, which permits all surface water to penetrate to the impervious bed-rock. Very few 

 springs occur, and those that do are intermittent except at the base of the hills. This condition 

 causes a wet layer to form at the surface of the bed-rock, and during periods of wet snow or 

 heavy rainfall avalanches result. — /. V. Hofmann. 



809. Ogura, Yudsuru. Some observations on the growth in thickness in trees, especially 

 with regard to that of Cryptomeria japonica. Bot. Mag. Tokyo 34: 81-109. 1920.— See Bot. 

 Absts. 7, Entry 1068. 



810. Olmsted, Fredrick E. National forest policies: a critical review of the several 

 plans. Jour. Forestry 18:598-609. 1920. — An analysis is presented of the manor features 

 of the national forest programs proposed by the United States Forest Service, the Ameri- 

 can Paper and Pulp Association, the National Lumber Manufacturers' Association, and the 

 Society of American Foresters. Of these, the last is preferred as it provides for direct national 

 control, and is far better than any state administration because of freedom from politics, 

 firmness of purpose, and efficiency. — E. N. Munns. 



