Rayner—Obligate Symbiosis in Calluna vulgaris . 
I2 5 
5. The ovary—and later the young fruit—contains mycelium in all 
parts of the internal tissues. This mycelium infects the seed-coats of the 
developing seeds. 
6. The embryo and endosperm of the resting seed are free from 
infection. 
7. By appropriate methods, seeds can be sterilized and seedlings 
germinated, free from fungal and bacterial infection. 
8. Failing infection by the appropriate Fungus, such seedlings do not 
develop roots ; they suffer complete inhibition of growth, remaining alive, 
but rootless, for several months. 
9. The mycorrhizal Fungus has been isolated from unopened fruits and 
from seeds removed from unopened fruits and has been grown in pure 
culture; sterile seedlings inoculated from a pure culture of this Fungus 
develop normally under aseptic conditions. The synthesis of Fungus and 
plant has thus been accomplished. 
10. In morphological characters the Fungus resembles the genus Phoma . 
In view of its distribution in the plant, and the unusual biological relations 
exhibited, it is proposed that the species described must be placed in a new 
sub-genus, for which the name Phyllophoma is suggested. 
11. Ovarial infection has been observed (and a similar distribution of 
the Fungus in the vegetative parts inferred) for a number of ericaceous 
species, including members of the Vaccinioideae. 
12. It has not been found possible to replace the stimulus to develop¬ 
ment which follows seedling infection by supplies of various organic 
nitrogenous substances in the food material. 
Discussion of Results. 
In view of the facts described in this paper, the conclusions of Stahl, 
with regard to the relations between ericaceous plants and their mycorrhizal 
Fungi, require revision. 
As a result of experimental work on Vaccinium, &c., germinated and 
grown in heath soil, sterilized by heat and by ether vapour, Stahl summarizes 
his conclusions as follows : 
‘ Wahrend manche obligaten Mycorrhizenpflanzen,wie wir friiher gesehen 
haben, der Anzucht aus Samen und der Kultur grosse Schwierigkeiten be- 
reiten, lassen sich die Ericaceen auch ohne Gegenwart von Wurzelpilzen 
unschwer kultiviren, und ihre Samen gehen, zwar oft langsam, aber in grossem 
Procentsatz und sicher ohne Mitwirkung symbiotischer Pilze auf ’ ( 16 ). 
According to Stahl, seedlings of Vaccinium Myrtillus sown in May, on 
soil which had been previously heated or treated with ether vapour, when ~ 
examined in October of the same year were completely free from fungal 
infection (‘ vollig pilzfrei ’). 
