LX. CHEMICAL NATURE OF THE SOILS OF N.S.W. 
that the addition of 1°5 per cent., making 2 per cent. in all 
(an amount which is above the average of the soils quoted 
by Hilgard), had very little effect indeed upon the texture 
of the soil when dried. It required the addition of at least 
3 per cent. (about 15 tons per acre 1 foot deep) to reduce 
the soil when dry to the crumbly condition characteristic 
of the soils of this region. It would seem, therefore, that 
some other cause, probably the absence of humus, operates 
in addition to bring about this state of things. This isa 
subject that will repay further investigation. 
Nitrification.—The nitrifying power of the soil is one of 
the most, if not the most, important index of its fertility, 
since not only does a vigorous nitrifying power ensure to 
the plant sufficient nitrates, which are essential to its 
proper development, but the conditions which promote 
nitrification, namely, aeration, moisture, and warmth, are 
exactly those which make for fertility. In this connection 
I will submit what Mr. Helms, who has given this subject 
his special attention, has to say on the matter. Nitrifying 
organisms appear to be present in all the soils examined, 
with the exception of swamp-soils on which water has lain 
for some period, and of extremely sandy soils. Sourness 
of the soil is detrimental to their growth, and, what is 
of special interest to our purpose, dryness of the soil 
affects the vitality of these organisms very strongly. In 
dry soils their vitality is considerably affected, and their 
development, when placed under favourable conditions, is 
very slow. When they have once started to develop, how- 
ever, their further growth proceeds fairly rapidly. It 
would appear that dry conditions, though they do not 
actually destroy the nitrifying organisms, reduce them to 
a dormant condition. The beneficial effects of irrigation 
were strongly marked in some samples from rice-fields near 
Bangkok. These were received in small hermetically-sealed 
