722 EXPERIMENT STATION EECOED. 



The proportions of lime to mag-nesia in the soil, and their relation to 

 nutrition in citrus trees, R. R. Snowdkn {Proc. Fruit Growers' Conv. Cal, 37 

 {1910), pp. 76-82). — The author claims to have traced several cases of mal- 

 nutrition, and specifically of incipieut chlorosis or " mottled leaf " in orange 

 and lemon trees, to an excessive proportion of magnesia to the lime in the soil. 

 A chemical examination of the ash from diseased lemon tree leaves showed a 

 potash content 2.5 times that in healthy leaves and a phosphoric acid content 

 11.5 times as much, while the lime showed a decided decline due, apparently, 

 to an excess of the magnesia in the soil compared to the lime available. 



The more rapid depletion of lime than magnesia by the processes of nutri- 

 tion apparently explains the fact that many citrus trees after flourishing for a 

 time ultimately show the effects of this relative exhaustion of lime. It is be- 

 lieved that the addition of lime to such soils would prove profitable. 



The efEect of cement dust on citrus trees, S. B. Parish {Plant World, 13 

 {1910). No. 12, pp. 288-291). — The author describes the condition of citrus 

 trees in the vicinity of cement works not far from San Bernardino, Cal. The 

 dust from these works is said to be detected at a distance of 3 miles, but its 

 seriously injurious effects are limited to a radius of about 1 mile. 



Investigations by means of glass plates coated with vaseline indicated that 

 the annual deposit of dust per acre in the orchards near the mills amounted to 

 from 2.39 to 3.18 tons. A microscopic examination showed that the dust was 

 deposited on the upper surfaces of the leaves and that the stomata were not 

 clogged, and there was consequently no evidence of interference with respira- 

 tion or transpiration. The cement covering of the leaves, liowever, by absorb- 

 ing dew forms a hard, opaque coating on the leaves, and this doubtless greatly 

 reduces their assimilating power. Where observations were made of deciduous 

 trees but slight injury was noted in comparison with citrus ti'ees. 



Some data are given relative to the apparent effect of the establishment of 

 these cement works on the indigenous flora, a considerable number of plants 

 which formerly were abundant having almost entirely disappeared. 



An efEect of cement dust on orang'e trees, G. J. Pierce {Plant World, 13 

 {1910), ISlo. 12, pp. 2S3-288). — The author describes his observations on the 

 effect of cement dust on orange trees in southern California, the presence of a 

 coating of cement deposited from cement works on the orange leaves resulting 

 in the reduction of starch in the me'jophyll cells to a very considerable extent. 



The observations confirm those previously noted (E. S. R., 22, p. 29) as to 

 the possible injury, and the author states that the more or less permanent coat- 

 ing of leaves which persist for 2 or 3 years, or possibly longer, with an opaque 

 crust, will produce a much greater and more continuous effect than a covering 

 on annual leaves, as described in the previous publication. 



Natural vegetation as an indicator of the capabilities of land for crop 

 production in the Great Plains area, H. L. Shantz {U. S. Dept. Agr., Bur. 

 Plant Indus. Bui. 201, pp. 100, pis. 6, figs. 23). — A study was made of the nat- 

 ural vegetation of the Great Plains area to determine whether it would form 

 a basis for a proper classification of the land for crop production. It is be- 

 lieved that the character of the natural plant cover can be used as a reliable 

 indicator of the conditions favorable or unfavorable for crop production, pro- 

 vided the relations between the vegetation and the environment are correctly 

 interpreted. 



On the Great Plains a pure short-grass cover indicates a condition of con- 

 siderable run-off and of limited water penetration, the presence of the short 

 grass being due to a growing season that is shortened by the limitation of the 

 water supply. Wire-grass land is characterized by a deeper penetration of the 



