184 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



by different causes in different cases. The only cause known with 

 certainty is the attack of the fungus Stereum purpureum. In other 

 cases silvering of foliage may be the result of physiological disturbances 

 unconnected with the action of any parasite, and the author quotes 

 as instances the silvery appearance of certain plum seedlings, and of 

 plants of the common white dead-nettle. He has been unable to 

 confirm Percival's view that the silvering of the fohage is the result 

 of the action of an oxidase, and supposes it to be due to interference 

 with the transpiration current. 



Not all trees attacked by Stereum purpureum develop the silvery 

 appearance characteristic of the attack in ' Victoria ' plums, for 

 example. The author states that he has seen trees of apple and 

 beech killed apparently by Stereum purpureum, but which had at no / 

 time shown any silver-leaf. At the same time cases are recorded, / 

 showing that the extent or intensity of silvering varies with different 

 varieties of trees. Experiments show that Stereum from a birch is 

 as effective in producing silvered plum leaves as is that taken frorr. a 

 plum. — F. J. C. 



Shading, The Effects oi Artificial, on Plant-growth in Louisiana. 



By H. L. Shantz (U.S.A. Dep. Agr., Bur. PI. Ind., Bull. 279 ; 

 April 1913, pp. 1-31 ; 6 plates, 11 figs.).^ — Experiments were 

 devised to (i) show the effect of different degrees of shade, giving 

 definite series of hght intensities, on plant growth ; (2) to show to 

 what extent the shade effects were independent of other physical 

 factors {e.g. temperature, humidity). 



Six different plants — radish, lettuce, potato, cotton, maize, 

 mustard — and six different intensities of light used. This was obtained 

 by using a framework with cloths of different texture, so as to give 

 five different degrees of shades (the sixth section was left uncovered 

 and so received full light). The experimicnt continued for fifty-one 

 days, the temperatures and humidity being recorded three times daily. 

 The following is a general summary of the experiments : 



1. When illumination decreases from J normal to f normal, a 

 general increase in growth resulted in potato, cotton, lettuce, radish. 



2. Corn made best growth in full light. 



3. When light was reduced to j\ normal or less, none of the plants 

 were able to manufacture food material to produce growth. 



4. When the solar energy was reduced to 10 calories per square 

 metre per second, or less, photosynthesis and growth practically 

 ceased. 



5. Effects of variations in temperature and humidity were so 

 shght that they could not be detected by comparison of control 

 plants. — A. B. 



Smoke and Gas Poisoning. By L. I. Knight and Wm. Crocker 

 (Bot. Gaz. May 1913, pp. 337-371 ; 4 figs.). — ^The authors used etiolated 

 epicotyls of pea seedlings, which are exceedingly sensitive to gaseous 

 poisons, in all their experiments. 



