G-1-2 JOUKNAL OF THE KOYAL HORTICULTUKAL SOCIETY. 



a few years the branch affected dies, and the silvering of the fohage 

 extends to other parts, until the tree is killed outright. The cause 

 was long unknown, but in 1902 Professor Percival showed by inocula- 

 tion experiments that it was due to the attack of a fairly common 

 fungus Stereum purpiireum, which usually fructifies in fallen trunks of 

 trees, especially poplars. Although it will grow on from year to year 

 in the tissues of a plant, it will never fruit until the wood of the host 

 is dead, but once the branch dies then, and not till then, it will produce 

 spores. When the silver-leaf disease brings about the death of a 

 branch tiny patches of fungoid growth appear on the surface of the 

 bark, and growing bigger gradually assume a purplish colour, though 

 it is occasionally white and pallid-looking, and takes the form of a 

 leathery earlike flap with wavy margins. Several of these arise together, 

 forming a stratified cluster; the upper surface carries an enormous 

 number of spores. To prevent the formation of these spores should 

 be the primary care of fruit growers. It has been shown at Woburn 

 that a living branch cannot transmit the disease. All wood should 

 therefore be removed and burnt as soon as it ceases to be alive. But 

 it is better to remove the whole branch as soon as silver-leaf appears, 

 burn it, and cover the cut surface with tar. There is no hope of the 

 branch getting rid of the disease, and no fimgicides are of any use. 



H. R, D. 



Soda, Nitrate of, in Horticulture, By Dr. A. Monnier {Jour. 

 Soc. Nat. Hort. Fr., series iv., vol. xii., July 1911, p. 371). — The con- 

 ditions under which the nitrates, so necessary a part of plant food, are 

 produced do not always exist in the soil. For nitrification to take place 

 the soil must be permeable to air, must contain a certain amount of 

 moisture, and must be at a temperature of from + 12° Cent, to 

 + 37°. It often happens in spring that the soil is not yet at 

 the temperature at which nitrification takes place, and young plants 

 suffer in consequence. At this moment it is indispensable to provide 

 azotic manure in some soluble and directly assimilable form, and of 

 these forms nitrate of soda is specially to be recommended, on account 

 of the rapidity of its effect. In horticulture it has not yet been suffi- 

 ciently appreciated, but it must be used with caution, as, according 

 to the quantity used, this substance becomes a food, a stimulant, or a 

 poison. The following are the different formulae suitable for different 

 purposes : — ■ 



For fohage plants in groups : — 



Nitrate of soda 50 grammes. 



Superphosphate of lime (12-14 per cent.) 75 ,, 

 Potassium chloride (per square metre) .15 



For flowering plants in groups: — 



Nitrate of soda 25 



Superphosphate of lime (12-11 per cent.) 125 

 Potassium cliloride (per square metre) . 25 



