477 
mountainous regions. They afford an explanation why a plant 
shuns calcium in one place and tolerates it in another; a sort of 
rivalry between allied species may also come into play here, as 
Náerrr has demonstrated with the familiar instance of Achillea 
atrata and Achillea moschata. 
In Goeree, however, none of these factors exist. The soil of both 
territories is sand, the grains being approximately of the same size, 
and the humus-content is low; in the sunlight the temperature does 
not differ materially in corresponding places; yet the drier grounds 
of the Land van Diepenhorst contain the plants under consideration, 
those of the Western-, and Central-dunes do not. Nor can the con- 
centration of the groundwater be the conclusive factor *), although 
generally speaking Gora’s classification, which lays special stress 
upon the contrasting characters of the colloidal and crystalloidal 
constituents of the soil, has many advantages. The xerophytic broom 
grows on the dry grounds of the Land van Diepenhorst; on the 
other hand it shuns the dry, as well as the moister sandy grounds 
of the Central dunes. In the former the concentration of the ground- 
water might be somewhat higher, and more stable on account of 
the slightly increased caleium-content, in the latter this is decidedly 
not the case, but both are pergeloid in Gora’s classification. Nevertheless 
it is obvious that the edaphic factors exert some influence here. 
The plant is capable of taking up considerable quanta even from 
a soil that contains very little calcium, thus the calcifuge Castanea 
vesca has on diluvial soil (calcium-content + 0.3 °/,) 45 °/, calcium 
in the ashes of the leaves, in those of the wood as much as 73°/,. 
The caleium-content of calcifuge plants is, however, mostly very 
low as may be demonstrated in a simple way with Motiscn’s *) 
reaction; formation of the double-salt Gaylussite by means of a 
10 °/, Na,CO,-solution. 
Calcifuge plants of the peat-moor, such as Drosera spec., Orchis 
maculata, Narthecium ossifragum, Gentiana pneumonanthe, Pingui- 
cula vulgaris, Molinia coerulea, Sphagnum spec. then yield a very 
faint reaction, Sarothamnus vulgaris likewise. From quantitative deter- 
minations [ gathered that the ash-content of this latter plant amounted 
to +16°/, of the dry weight, the calcium-content of the ashes 
=0.0°/,, that is 0.5°/,, of the dry weight. We see, then, that, 
though the ash-content of a plant and also the amount of calcium 
in the ash varies largely with the nature of the soil on which it 
1) G. Gora. Saggi di una teoria osmotica del edafismo. Ann. di Bot. VIII 1918. 
2) H. Morrscr, Beiträge zur Mikrochemie der Pflanze. Ber. d. Bot. Ges. 1916. 
31 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
