130 Rayner.—Obligate Symbiosis in Calluna vulgaris . 
5. Nutrient Agarl + 10 acidity. 
Twenty days’ culture. Colony 3 cm. diameter. 
Thirty ,, „ Colony 3-25 cm. diameter. 
Forty „ „ Colony 3-5 cm. diameter. 
Colony yellowish, raised, with very scanty growth of mycelium on surface. 
Colour of the medium unchanged. Mycelium showing a preponderance of the 
larger hyphae, in which the cross-walls are strongly marked ; branches often ‘ jointed ’ 
in structure; no separation of chlamydospores observed (PL VI, Fig. 21). 
The mycelium shows a vigorous development of large swellings—terminal, inter¬ 
calary, and in chains. 
6. Nutrient Agar, —5 alkalinity. 
Twenty days’culture. Colony 1*5 cm. diameter. 
Thirty „ „ Colony i*8 cm. diameter. 
Forty „ „ Colony 2*0 cm. diameter. 
No further growth. Colony similar in appearance to last, but the medium 
tending to deepen in colour. 
Mycelium as last, with very conspicuous development of swellings. 
Hydrolysis of arkutin. The glucoside arbutin is widely distributed among the 
members of Ericaceae. 
It occurs abundantly in the tissues of Calluna ; in a watery extract of the leaves 
and young shoots made in the cold, the colour, at first yellowish, slowly deepens until 
the solution becomes dark brown. 
This browning of the extract is presumably due to hydrolysis of the glucoside to 
glucose and hydroquinone, the latter of which oxidizes to form a brown pigment. 
The browning of the plant-cells in unhealthy seedlings is possibly due to related 
causes. 
The production of an enzyme by the Fungus able to effect the hydrolysis of 
arbutin has been determined by transferring mycelium from a pure culture on rice to 
tubes containing a 0-5 % solution of arbutin. At the end of a week the tubes showed 
slight browning of the solution, the coloration gradually becoming more marked. 
Control tubes, containing a 0-5 % solution of arbutin without the Fungus, remain 
colourless. 
List of References. 
1 . Grabner, P. (TO) : Lehrbuch der allgemeinen Pflanzengeographie, 1910, p. 236. 
2 . Rayner, M. C., and Jones, W. N. (’ll) : Preliminary Observations on the Ecology of Calluna 
vulgaris on the Wiltshire and Berkshire Downs. Soil analyses by J. W. Tayleur. New 
Phytologist, vol. x, Nos. 7 and 8, 1911. 
3 . Rayner, M. C. (T 3 ): The Ecology of Calluna vulgaris. New Phytologist, vol. xii, No. 2, 
l 9 l $- 
4 . Kamienski (’ 81 ) : Die vegetativen Organe der Monotropa Hypopitys. Bot. Zeit., Bd. xxxix, 
1881, p. 457. 
- (’ 84 ): Les organes vegetatifs du Monotropa Hypopitys. Memoires de la Soc. des 
Sc. de Cherbourg, t. xxiv, 1884. 
1 The nutrient agar was made up with Lemco and standardized in the usual way. 
