Rayner.—Obligate Symbiosis in Calluna vulgaris. 123 
Unless otherwise stated, all the cultures described were made from this 
original sub-culture on rice, and were kept at room temperature. 
The morphological characters of the Fungus agree with those of the 
genus Phoma. 
They coincide generally with those described for the five pycnidia- 
forming Fungi, isolated from the roots of five ericaceous species by a previous 
observer ( 26 ), and referred to this genus. 1 In view of the anomalous distri¬ 
bution in the tissues of the plant, and the fact that the members of the 
genus Phoma, as commonly understood, are obligate parasites in all parts 
of plants except the leaves , it is suggested that the species now described 
should be placed in a new sub-genus Phyllophoma. 
With regard to the physiology of the Fungus, many problems present 
themselves. 
The reaction of the micro-organism to acid and alkaline media and 
to various soil extracts ; the possible excretion of acid by the Fungus when 
grown on various substrata ; a more detailed knowledge of the nature of the 
enzymes produced ; and the behaviour of the Fungus in pure culture when 
inoculated with Bacteria present on the roots of plants growing in calcareous 
soil, all suggest lines of research of special interest from the point of view 
of the ecology of the plant. 
The Distribution of the Endophyte in other Species 
of Ericaceae. 
A number of other ericaceous species have been investigated in order 
to determine whether the condition described for Calluna is common to 
other members of the order. 
In every species examined, mycelium could be identified in the ovary 
of the unopened flower—in many cases removed from the resting bud for 
examination—which showed relations with the plant tissues similar to those 
described for Calluna . It has not yet been possible to make a detailed 
examination of the vegetative tissues in each case, but in some of the 
species the endophyte is undoubtedly present in the leaves also. 
The ease with which mycelium can be demonstrated varies very much. 
In the members of Ericoideae it is usually extremely reduced and difficult 
to recognize in the tissues. 
Since the list of species appended contains representatives from the 
Rhododendroideae, Arbutoideae, and Vaccinioideae, as well as from the 
Ericoideae, it seems reasonable to conclude that the distribution of the endo¬ 
phyte described in detail for Calluna is common to all members of Ericaceae. 
The agreement of members of Vaccinioideae in this respect is of interest 
1 It is doubtful whether any of these species can be identified with certainty with the species of 
Phoma recorded by Rabenhorst from members of Ericaceae (see Ternetz, 26). 
