320 JOURNAL OF THE ROYAL HORTICULTURAL SOCIEf Y. 
roots. Experiments show that plants grown in a beaten-down soil 
are poor and stunted in comparison with those grown under similar 
conditions in an open soil. The effect of soil aeration as a controlling 
factor is too often overlooked in pot and field experiments, and it 
requires to be further worked out as affecting disease. 
The fundamental question of food-constituents and the associated 
theories of manurial treatment, though much discussed, remain in a 
state not altogether satisfactory, and there is room for a more scientific 
basis of experiments. 
Nitrogen may be cited as one of the most important of the food 
elements which is liable to abuse. Much has been written about the 
supply of combined nitrogen, but the harmful effect of excessive 
nitrogen has not received the attention it deserves. Numerous cases 
can be indicated in which plants are rendered specially susceptible 
to fungus diseases through the improper use of this element. 
Potatos which have received an excessive application of nitrogenous 
manure show a greater development of stem and leaf, and consequently 
a greater amount of chlorophyll, but at the same time there is an 
expenditure of plastic material, and therefore less starch storage in 
the tubers. The quality of the potatos is thus reduced, accompanied 
by a greater tendency to disease, not only in the vegetative growth 
but also during storage. 
In Sugar-beet excessive nitrogen, while increasing the weight of 
the crop, at the same time diminishes the sugar content and lowers the 
power of resistance to disease. 
In the case of fruit trees, a comparison between plants treated 
with latrine manure and with potassium phosphate showed with the 
former a smaller quantity of fruit but greater susceptibility to frost ; 
as regards Apples, a tendency to attack by woolly aphis, and in the 
orange to " die-back " and insect pests. 
In the raising of Gooseberry plants from cuttings it has been the 
aim of the cultivator to produce a saleable, stocky plant, and to induce 
the necessary growth nitrogenous manure is applied. Observations 
seem to show that the Gooseberry mildew is associated with this 
method of cultivation, whereas on poor soils this disease is much less 
frequent. 
With Roses the custom of an annual mulch is followed by an 
annual appearance of mildew. 
In Quick (Crataegus) the appearance of mildew has also been 
associated with manuring, while the surrounding hedges were free. 
In the case of greenhouse plants, the prevalence of Botrytis and 
other diseases has been traced to excessive nitrogen. Similar observa- 
tions have been made with regard to vegetables. These, when 
over-manured, are more prone to disease and degenerate in flavour. 
Mention may be made of a Tomato-house where the plants had been 
treated to a heavy mulch, with the result that the entire crop was 
ruined by an attack of Cladosporium. 
With regard to such elements as potassium and phosphorus, the 
