61 
THE WATER-CONTENT OF ACIDIC PEATS.* : 
W. B. CRUMP, M.A. 
RECENT ecological researches all emphasise the importance 
of edaphic factors in determining the distribution of plant 
associations, and the complete lack of exact data based upon 
quantitative experimental work. While the nature of the soil 
and the richness or poverty of the soil-water in nutrient salts 
are factors of primary importance, the water-content would 
seem to be of equal importance. As regards this soil-water it 
is recognised that some of it, possibly much of it in acidic or 
saline soils, is not available to plants, so that the determination 
of the available, or what Schimper has termed the physio- 
logical, water is also desirable. The last point is considered 
in another paper [see page 343], the other factors are eliminated 
by selecting a series of habitats exclusively on siliceous rocks 
with the soil-water deficient in soluble salts, but always more 
or less acidic through the presence of humus acids. As the 
alkaline peats differ in all these respects and support totally 
different vegetation, their consideration is reserved. 
The peats examined were all obtained on the moorlands of 
the Southern Pennines, and mostly in the neighbourhood of 
Halifax. The sample was selected from the zone of active root 
absorption, and if not apparently homogeneous it was divided 
into layers. It was taken during dry weather—never within 
a few days of any rainfall—with the purpose of obtaining the 
minimum value. The water-content is exclusively the water 
that evaporates when the peat is exposed to the air at or about 
15° C., and the results are expressed in terms of such air-dry 
peat. The peat was then oven-dried and subjected to com- 
bustion to determine the humus and mineral residue. This 
not only graded the peats, but eventually furnished the solution 
of the problem. Without a knowledge of the humus-content 
the water-content was meaningless, and the analyses widely 
discordant. But the ratio Water-Content seduces them to 
Humus-Content 
order. This is most evident in dealing with successive layers 
of the same section, e.g., a peat containing 170 per cent. of 
water lies immediately above a sandy sub-peat with only 30 
per cent., and the fine rootlets of bilberry penetrate both. 
But the ratio, or water co-efficient, is practically the same for 
each, viz. 3-0 and 2:9. So, again, the ratio will reveal superficial 
drying by its low value when the actual water-content may 
be very high. 
The ratio H¥™S js also 'a convenient way of expressing the 
Mineral 
humus-content of the peat. 
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-* Abstract of Paper read at the Portsmouth Meeting of the British 
Association, the full text of which will appear elsewhere shortly. 
tg1t Oct. I. 
