F, B. GUTHRIE. LXIII. 
Fertility.—To sum up the conditions which determine 
fertility they are :— 
Sufficiency of plant-food, of humus, and of water. 
A proper proportion between the amounts of sand and 
clay. 
An open texture which allows of free passage of air 
and water, and is sufficiently close to allow of 
capillary action. 
On the texture depends the power of the soil for retain- 
ing water, its nitrifying power to a large extent, the solvent 
power of the soil-water, and the maintenance of an equable 
temperature. All these conditions are threatened if water 
is absent, and all are improved under irrigation if properly 
carried out. 
Irrigation Fertilises.—Irrigation is of value also on 
account of its direct fertilising effect, since all water con- 
tains more or less saline matter in solution, which is retained 
by the soil, and acts as plant-food. 
Injurious Substances.—There are, however, certain 
waters which contain substances which in quantity are 
injurious to plant-life, and such waters must be employed 
with caution. The most commonly occurring of these 
substances, as far aS we are concerned, are common salt 
and carbonate of soda. These salts have an injurious effect 
both upon the plant and upon the soil. 
We have found by direct experiments in pots that the 
growth of wheat is affected by quantities as low as ‘05% 
to 15% of common salt, whilst ‘2% prevented germination.’ 
Carbonate of soda (alkali) affects the growth of the plant 
when present to the extent of °1%; °3% prevents germination 
and growth. The efiect of alkali upon the soil has been 
brought under your notice already by Mr. Boultbee, in his 
quotations from Prof. Hilgard, who is our principal authority 
' F. B. Guthrie and R. Helms—Journ. Ruy. Soc. N.8S.W., XxxXvVI., p. 191. 
