Orchid Mycorrhiza. J. Ramsbottom. ‘47 
fungi in nature except so far as they occur associated with 
rooted orchid plants. Probably most people are aware that 
fungi of all kinds are present in the soil, but few realize in what 
enormous numbers they occur and the manner in which some 
are restricted to the soil. Hagem* calculated that in a gram of 
soil from a potato field, 350 spores of Rhizopus stolonifer and 
250 each of Mucor sphaerosporus, M. nodosus, Absidia cylindro- 
spora and Zygorhynchus Moelleri were present; and these 
numbers are much exceeded by Penicillium (go—95 per cent. of 
spores in uncultivated soil according to Soppt) and other 
Hyphomycetes. Traaenf calculated that from 10,000 to 120,000 
spores of Geomyces vulgaris and from 1000 to 20,000 spores of 
Humicola fuscoatra occur in a gram of soil. Much work has been 
done recently on the biological activities of such fungi, attention 
being paid chiefly to cellulose destruction and the possibility of 
nitrogen fixation. It is extremely probable that certain of the 
forms isolated are capable of acting as mycorrhizal fungi, though 
none have apparently been recognised as such. Further it is 
possible to isolate Rhizoctonia from the soil in the immediate 
neighbourhood of orchid plants growing wild (as also from the 
soil of pots containing cultivated orchids): but notwithstanding 
the large number of species of soil fungi isolated it does not 
appear to have been found, or at least recognised, by any in- 
vestigator. We are thus lacking in data as to the distribution 
of orchid fungi in the soil. Since, however, Bernard isolated 
Rhizoctonia repens from many European orchids and showed it 
to be the commonest endophyte amongst cultivated species, it 
must be of world-wide distribution, since in order to account 
for the distribution of the orchids it is necessary to assume that 
this particular fungus must occur practically wherever orchids 
grow. 
ERICACEAE. 
A family of plants which is usually linked with orchids as 
showing the same constancy of fungal infection is the Ericaceae. 
Frank early realized that the relation between the fungus and 
flowering plant in these two families is a particularly close one. 
In certain ericaceous plants he remarked on the absence of 
root-hairs, the absence of, or reduction in, the amount of cortical 
tissues, the reduction of the root- -cap, and the masses of fungus 
mycelium in the enlarged cells of the epidernial layer. Ternetz§ 
* OQ. Hagem, Untersuchungen iiber Norwegische Mucorineen II. Skrifter 
Vidensk.-Selsk. Christiania. I. Math.-Natur. Kl. No. 4 (1910). 
t ms J.O.Sopp, Monographie der Pilzgruppe Penicillium. Idem, No. 11 (1912). 
A. E. Traaen, Untersuchungen iiber Bodenpilze aus Norwegen. Nyt 
Mag. Naturvidensk. LII. pp. 19-121 (1914). 
C. Ternetz, Uber die Assimilation des atmospharischen Stickstoffes durch 
Pilze. Jahrb. f. wissensch. Bot. xLiv, pp. 353-408 (1907). 
