384 SECTIONAL TRANSACTIONS.—K. 
detail, and evidence has been obtained which shows that three possible 
interactions may take place—the presence of the first virus may (a) affect 
(often making more severe) the symptoms induced by the second virus, 
(b) prevent the appearance of symptoms characteristic of the second virus, 
which nevertheless multiplies in the tissues, or (c) prevent the multiplication 
of the second virus in the tissues. 
Dr. Mary J. F. Grecor.—A disease of Bracken and other ferns caused by 
Cortictum anceps (11.5). 
Corticium anceps is a vigorous parasite of Bracken in moist, shady situations. 
It has once been found attacking Male Fern, and infection experiments 
indicate that the Prickly Shield Fern is also to some extent susceptible. 
The disease occurs almost exclusively upon the frond of the Bracken and 
has never been seen to extend more than a few inches down the petiole ; 
it does not attack the rhizome. The fungus creeps over the lower surface 
of the pinnz and rachis and at first remains entirely superficial. Soon, 
however, penetration of the host is effected, mainly by means of infection 
cushions, though individual hyphz often enter through the stomata. ‘The 
external mycelium continues to spread and ultimately forms a whitish 
felt-like covering over the lower surface of the frond. ‘The infected tissues 
become brown and brittle, and in severe cases the pinne break off, leaving 
only the bare discoloured rachis. In the later stages of the disease sclerotia 
and basidia are developed upon the superficial mycelium. The parasite 
grows readily in culture and forms typical sclerotia, but no basidia. The 
basidiospores germinate in culture by means of a germ tube, but when 
germinating in situ on the hymenium they sometimes form secondary spores. 
Dr. Epitu P. Smira.—The ecology of the island of South Rona (11.35). 
South Rona lies between Skye and the mainland; it is about 44 by 
14 miles, and reaches a height of 404 ft. There are steep cliffs on the east 
side and two large inlets (Big Harbour and Dry Harbour) on the west side. 
The island consists of worn Lewisian gneiss, in a series of rocky ridges and 
valleys running north-west to south-east. ‘There are few streams, and 
only two small bodies of water: one of these was newly recorded. The 
vegetation is sparse, of moorland type mainly, merging into cotton-grass 
bog on upland valleys, and marsh (salt and fresh) on west coast. East cliffs 
are topped with bracken-invaded pasture. No natural woodland except 
scrub birch and willow, but remains of Pinus sylvestris wood in a peat bog, 
and a submerged forest (mainly alder and birch) were located at Dry 
Harbour. Once supported a population of 159; present population, 3. 
The abandoned arable had become a pure society of Juncus communis. 
A ‘ sea-weed farm’ (to supply manure for fields) was located at one of the 
deserted villages. Slight differences in the content of the moor flora on 
tertiary intrusions were noted. 
Dr. Oxtve D. Dicxinson.—The distribution of certain constituents of the 
flora of Bas-Languedoc (12.5). 
A study has been made of 140 species in Bas-Languedoc showing dis- 
jointed distribution, which appears impossible of explanation by dissemina- 
tion under existing conditions. ‘The majority are distributed throughout 
the Mediterranean basin, including the islands of the Mediterranean Sea ; 
and all are species of clearly defined—often very isolated—systematic 
position indicating their ancient character. 
