The Ecology of Calluna vulgaris. 239 
fertile soils are recorded from other districts with a comparatively 
high proportion of magnesia. 
Sufficient data, however, are not available at present to warrant 
any definite suggestion as to the significance of the decreased 
amount of magnesia in D from which Calluna is entirely absent. 
Experiments dealing with the proportional amounts of magnesia 
and calcium carbonate in the soil have been recently carried out on 
wheat and barley at the Woburn Experimental Station (9). The 
earliest experiments were made on pot plants and were followed by 
field experiments with similar results. 
Starting with a soil containing magnesia and calcium carbonate 
in the proportion of 1 : 2, it was found that as the magnesia was 
increased so the inferiority of the crop became more marked. 
Vegetative peculiarities were noticed, such as the development of 
an abnormally extensive and fibrous root-system, the soil became 
darker in colour, and rather more sticky and retentive of water. 
These results have not been confirmed by other observers up to the 
present. 
The observations of Loew (11) on the physiological role of 
calcium and magnesium salts in plants are also of interest in this 
connexion. Recent papers by Konowalow (12) and Lemmermann 
(13) are not in agreement with Loew’s conclusions nor with the 
results of the Woburn experiments. 
Konowalow working with sand and water cultures, is of the 
opinion that observed differences in growth must be attributed to 
varying concentrations of the solutions. 
Lemmermann concludes from field experiments on various 
crops, that the ratio of CaO: xWgO may be altered within wide 
limits without appreciably affecting the crop. He finds, however, 
that dressings with lime and magnesia affect absorption of phos¬ 
phoric acid, in the direction of increased phosphoric acid absorption 
with increased proportion of magnesia. 
He finds also that the micro-organisms of the soil were un¬ 
affected by changes in the CaO : MgO ratio. 
Our experiments during the past year with Calluna in arti¬ 
ficial cultures and in pot cultures of the Botley soils, suggest thnt 
a soil factor is present which affects the germination of the two 
seeds and also the subsequent growth of the seedlngs. They are 
inconclusive at present as to the significance of magnesia in this 
connection. 
Since relations with the soil are peculiar in Calluna and in 
