The Acidity of Sphagnum and its Relation to Chalk 
and Mineral Salts. 
BY 
MACGREGOR SKENE, D.Sc., 
Lecturer on Vegetable Physiology , Aberdeen University. 
I N the study of the influence of the chemical nature of the soil on vegeta¬ 
tion the question of the effect of calcium carbonate—chalk—has always 
occupied a prominent position. It is one of the soil constituents which can 
be most easily recognized and estimated ; and the differences in the flora, 
of which its presence or absence is the cause, are frequently very striking. 
Lists have been compiled of plants which thrive only on chalk (calcicole), 
and of others which cannot live in its presence (calcifuge). Such plants 
may be wholly confined to the one type of soil or to the other ; or their 
behaviour may change with change in other external factors. Reference 
may be made to Nageli’s (’ 65 ) classical case of the calcicole Achillea 
atrata, and the calcifuge A. moschata. When the two occur together in the 
same valley, each is strictly confined to its own type of soil; but if either 
occurs in absence of the other, it is non-discriminating. Another case of 
great interest is that of Castanea vesca, the Sweet Chestnut, which cannot 
grow on chalk unless an abnormally high percentage of potassium be present 
in, or be added tt> the soil (Arnold Engler, -’01). 
Perhaps the majority of plants written down as calcifuge belong to this 
indeterminate type ; but there is a number of cases in which the repugnance 
to chalk is constant, and independent of other external factors. Of these 
one of the most striking examples is afforded by the genus Sphagnum^ 
the members of which are rapidly killed off by water containing calcium 
carbonate. 
Observation of the fact that chalk can exercise so marked an effect on 
vegetation has led to the attempt to find out exactly in what manner the 
chalk acts. Such investigation has shown that it acts in a number of quite 
distinct ways. 
Its effect may be indirect. This seems to apply to Callima, studied 
by M. C. Rayner (T 3 ). She has shown that the presence of chalk interferes 
with the proper development of the mycorhiza, and promotes the growth of 
a bacterial sheath on the roots. This interference with the root symbiosis 
[Annals of Botany, VoJ. XXIX. No. CXIII. January, 1915.] 
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