510 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



3 plates, 5 figs.). — The pear thrips has been fourd only near San 

 Francisco Bay. The adults injure the trees by rasping the tissues and 

 sucking the sap from the young buds and blossoms. 



If land is ploughed as soon as possible after the early rains in 

 October, November, and December, to a depth of seven to ten inches, 

 and afterwards well harrowed, the pupse are broken from their pro- 

 tecting cells and injured or killed. 



Sprays of tobacco-extract in combination with oil emulsion should 

 be used in early March and again in April. — V. G. J. 



Peat Mosses, Plants in. {Bot. Gaz. vol. xlix. pp. 325-339; 

 May 1910). — The full title of this paper is *' Physiologically Arid 

 Habitats and Drought Resistance in Plants." 



The author found that in samples of bog water kept in a well- 

 corked glass jar (at 20-^-25° C. and in the dark) methane and other 

 gases are developed. In a few weeks a thin surface layer formed on the 

 liquid, which consisted of bacteria embedded in a matrix. The exclusion 

 of air prevents further growth of the bacteria, which are aerobic. 



Litre flasks containing a sterilized solution of bog water were then 

 infected with pure cultures of some thirty-five species of these bacteria 

 which had been isolated by the author. As a control he retained several 

 flasks with the sterilized solution, and which were not inoculated. 

 Some flasks were also infected with 1 c.cm. of fresh bog water in the 

 litre. 



Wheat seedlings, specially prepared, were grown, in all these solu- 

 tions. The transpiration was found to be much reduced in those plants 

 grown in bog water, being only 30*79 per cent, of that given by plants 

 in the control flasks. In the bacterial cultivation the transpiration 

 was also much less than in the controls, being only from 68 to 79 per 

 cent. 



In some of the pure bacterial cultivations indol and ammonia were 

 produced, but no further decomposition occurred. In the bog water 

 solution amido-acids were further transformed, yielding ammonia and 

 compounds of the fatty acid series. Some of the bacteria also decom- 

 pose carbohydrates, for if air is admitted litmus paper may be dis- 

 solved, but these were not isolated. 



It seems that a whole series of bacteria are concerned in the process. 

 The injurious products of this bacterial bog-flora accumulate in definite 

 layers of the peat. 



These toxic substances are retained in soils used for filtering bog 

 water. Plants grown in such contaminated soil were deficient in dry 

 weight to the extent of 18 per cent, in sand, 3 per cent, in clay, and 

 36 per cent, in humus. ' 



It is these poisono s products w^hich prevent some plants from 

 colonizing bog water or bog soil and interfere with the proper develop- 

 ment of others. Some plants can accustom themselves to such toxic 

 substances. By rearing plants in gradually intensified toxic solutions 

 they may acquire a much higlier resisting power than they possess when 



