NOTES ON RECENT RESEARCH. 



1111 



would it not be possible to introduce into the body of the plant small 

 quantities of sulphate of copper or some other equally efficacious 

 substance, and thus render the tissues refractory to the development of 

 mildews ? 



Special experiments were conducted for the purpose of rendering 

 Lettuce immune to the attacks of Bremia lactucce, the Lettuce mildew. 

 These experiments were made with two objects in view : the action of 

 the salts experimented with on the vitality of the Lettuce, and on that of 

 the parasite. 



Sulphate of Copper. — Lettuce grown in a nutrient solution containing 

 1 oil oil t° i oo()0 °f this salt showed variable results, depending on the 

 rapidity of growth, temperature, bygrometric condition of the air, and 

 amount of light. Sometimes growth was sensibly retarded, and it was 

 found necessary to use not more than lu „ 00 to ,„■;„„ to secure normal 

 growth of the Lettuce. 



Lettuce grown with I() ;'; (M ) to 1(l() 7 00 of sulphate of copper completely 

 resisted infection. Sometimes the cotyledons were slightly attacked, but 

 the leaves proper proved to be absolutely immune. 



Lettuce treated with 10 j{ u0 to Io( ' l)0 of the same salt, showed a 

 marked resistance to infection. This resistance totally disappeared when 

 the amount of copper was reduced to 



Certain other salts, as sulphate of iron and sulphate of manganese, 

 were also experimented with, but proved in every case inferior to sulphate 

 of copper. 



A series of experiments conducted for the purpose of determining the 

 effect of nutritive salts, as influencing a predisposition to disease or other- 

 wise showed that nitrates and phosphates favoured the attacks of the 

 Bremia, whereas potassium salts enabled the Lettuce to resist such 

 attacks to a marked degree. 



As a result of these experiments, it is considered that by means of 

 absorbing certain fungicides through the root, more especially sulphate of 

 copper, Lettuce can be rendered immune against the mildew known as 

 Bremia lactucce. 



Unfortunately, there are difficulties yet to be overcome before these 

 processes can be practically applied on a large scale ; the most serious of 

 which consists in the comparatively narrow margin between the amount 

 of sulphate of copper required to secure immunity from the mildew, and 

 that amount which the Lettuce can bear without injury. 



Notwithstanding these present difficulties, the author considered that 

 further experiments may lead to a successful issue, and that not only 

 Lettuce but also other plants may be rendered immune against their 

 respective mildews through the absorption of mineral salts by the roots. 



G. M. 



Effect of Manganese. 



Manganese Compounds, Action on Plants of. By 0. Loew, 

 K. Aso, and S. Sawa (Flora, vol. xci. 1902, pp. 2G5-273 ; 1 fig.). — 

 Manganese is known to be an important constituent of plants, often 

 exceeding iron. Thus the ash of Birch-leaves gave 14*47 per cent. 

 Mn ;j 0 4 , and only 1*43 per cent. Fe 2 0 3 ; that of needles and bark of 



