66 
Skene.—The Acidity of Sphagnum and its 
is accompanied by symptoms of weakness on the part of the Calluna , and is 
apparently responsible for these. 
A more direct influence must be assumed in other cases. This may be 
either physical or chemical. 
Kraus (’ll) has demonstrated very completely the effect of chalk on 
the water content and temperature of the soil; the former is diminished, 
the latter increased as the amount of chalk present rises. And he has 
shown that a number of plants typically found on chalk can grow equally 
well on siliceous soil, if its physical properties resemble those of the chalk. 
I am inclined to believe that a case illustrating this is afforded by the 
distribution of Helianthemum Chamaecistns in this country. The Rock 
Rose is generally described as a calcicole plant (see * Types of British Vegeta¬ 
tion ’, Tansley, p. 176). It is common, however, and grows well on siliceous 
gravels in exposed situations in the east of Scotland. In the south of 
England, where the choice may lie between dry warm chalk and cold wet 
clay, the former is chosen ; where there exists a siliceous soil, which is also 
well drained and warm, Helianthemum can thrive thereon. 
Cases in which the chalk acts chemically are also known. The fact 
that Castanea can grow on chalky soil when supplied with an abnormally 
large amount of potassium, indicates that the chalk acts by interfering with 
the supply of other salts through the roots. Moreover, the Chestnut 
grafted on the Oak can grow even on normal chalk soils—a further support 
of this view (see Jost, T 3 , p. 125). Schimper (’ 98 ) states that in some 
cases the failure on chalk is due to difficulty in absorbing sufficient iron, and 
may be obviated by watering with iron solutions. 
Another extremely important effect of the chalk is that it alters the 
reaction of the soil, rendering it neutral or alkaline. To this is probably 
due its noxious effect in many cases. It will be shown that there are 
grounds for ascribing its fatal action on Sphagnum to this cause. 
The earlier observations on Sphagnum and its relation to chalk have 
been collected by Paul (’ 08 ), and as most of them have been published in 
periodicals not readily accessible to English readers, a short summary may 
be of use. 
Sprengel (’ 47 ) asserted that Sphagnum could not support high concen¬ 
trations of any mineral substances. Sendtner (’ 54 ) was unable to grow it in 
chalk water, and concluded that basic substances were harmful. Milde (’ 61 ) 
concluded from observations in the field that Sphagnum is calcifuge. 
Pfefifer (’ 71 ) notes that it dies in presence of chalk. Ohlmann (’ 98 ) found 
that it dies in a 0*05 per cent, solution of chalk, the time elapsing before 
death varying with the species used. To produce the same effect with 
calcium sulphate a solution of twice that strength was necessary, while of 
calcium nitrate a 0-75 per cent, solution was required. Culture solutions 
