370 
The British Association at Dundee. 
aceae is to be sought in a monostelic form such as Sutcliffia, rather 
than in the polystelic members of the Medulloseae. 
Mr. H. Hamshaw Thomas described Marattiopsis anglicn, a 
new Jurassic member of the Marattiaceae which further indicates 
the great antiquity of that group. 
Dr. Agnes Arber contributed a brief account of a new type of 
Lepidostrobus , possessing large sterile processes within the sporan¬ 
gium. 
Other Papers. 
A most interesting communication was made by Dr. Ostenfeld 
of Copenhagen dealing with experiments on the origin of species in 
the genus Hieraciuni. This paper appears in full in the present 
issue of the New Phytologist. 
Professor F. E. Weiss gave an account of his experiments in 
breeding Geum intermedium. This form can readily be obtained by 
crossing Geum urbanum with Geum rivale and exhibits a remarkable 
blending of the characters of these plants. Its colour, for example, 
is due to the possession of both the epidermal anthocyanin of G. 
rivale and the yellow plastids of G. urbanum. The hybrid is perfectly 
fertile and both F 2 and F 3 generations have been raised. The Fj 
generation does not vary very much, but in the F 2 generation the 
segregation of a number of important characters takes place, e.g., the 
curvature of the peduncle, the presence of anthocyanin, the form of 
the calyx and petals. In the discussion it was pointed out that 
Professor Weiss’s observations probably indicated the type of 
variation which had led to the appearance of the existing forms of 
the allied genus Rubus, while on the other hand Dr. Ostenfeld had 
indicated that the polymorphism of the Hieracia was due to entirely 
different causes. 
Miss M. C. Rayner gave an account of her work on the ecology 
of Calluna vulgaris, in which the results of some experimental 
cultures, undertaken in order to throw light on the soil-preferences 
of this plant, were indicated. In water cultures the seedlings grow 
equally well in neutral or faintly acid solutions, but are very sensitive 
to changes in the concentration of the culture fluids. In pot cultures 
with soil from the chalk-down outside the heather area growth is 
retarded and germination capacity is lowered ; bacterial colonies, 
often forming a sheath round the root-tip, are prominent on the 
roots of young seedlings. In sterile agar cultures, using extracts 
from the heather and chalk-down soils, unsterilised seeds show a 
growth of micro-organisms, chiefly mycelium with the former extract, 
and bacteria with the latter. The problem is then to discover if 
the peculiarities of Calluna are specific or if they depend on 
mycorhiza and the bacterial flora of the soil. Towards the solution 
of this question, it has been found that seedling roots are normally 
infected soon after germination by a mycorhizal fungus arising from 
the seed-coat. Seeds can however be sterilised and germinated on 
agar plates. Under such conditions germination takes takes place 
normally and the seedlings start growth in the usual way. 
Mr. Macgregor Skene in dealing with the relation of Beech 
forest to edaphic factors, compared the English type on chalk with 
that growing at high altitudes in the Cevennes on schist free from 
