48 Transactions British Mycological Society. 
was successful in isolating the fungi from certain species and 
growing them in pure culture, constantly obtaining the same 
fungus from the same species of flowering plant. All the fungi 
belonged to the genus Phoma*—one of the Fungi Imperfecti, 
but of a totally different group than is Rhizoctonia—and were 
apparently morphologically and physiologically distinct. She 
showed that infection of Calluna took place in the seedling and 
also found infection in a case of viviparous germination in 
Andromeda. 
Rayner working with Calluna vulgaris was able to show that 
the full development of the seedling was dependent upon the 
presence of the mycorrhizal fungus—there is here an “obligate 
symbiosis” of a type very similar to that in orchids. Finding 
that the sterile seedlings were unable to form a root-system she 
investigated the matter in the manner made classical by Bernard. 
The seed coats were found to become infected while the seeds 
are still in the ovary. Delicate branched hyphae are present in 
the cells of the ovary wall, in the tissue of the central column 
and in the funicles of the seeds. Branches of this mycelium grow 
across from the cells of the ovary wall to those of the seed-coats, 
extending from one seed to another. The fungus was isolated 
and grown in pure culture. It proved to be a pycnidial form 
similar in all respects to the genus Phoma. Sterile seeds sown 
on this develop normally, whereas in its absence the seedlings 
merely form a few reddish or chlorotic leaves, but no roots. 
Infection of the seedling roct takes place at, or immediately 
after, it emerges and may begin at the tip by hyphae forcing 
their way between the cells of the apex, though more usually it 
occurs simultaneously at several points. The mycelium im- 
mediately becomes intercellular and infection spreads rapidly 
from cell to cell. Some hyphal branches grow out and infect 
fresh rootlets as they develop; others form a tangled skein of 
fine hyphae in the superficial cells. One of the most interesting 
points of the story is, however, that the fungus does not remain 
confined to the roots but infects the whole of the young seedling. 
In the subaerial parts the mycelium does not develop so ex- 
tensively on the surface of the plant, nor do the hyphae become 
balled up in the superficial cells as in the roots, but are irregularly 
distributed in the tissues. In the mature plant likewise the 
fungus is not confined to the roots but is present in the tissues 
of the stem, leaf, flower and fruit. The hyphae can also be seen 
ramifying among the hairs or closely applied to the cuticle of 
* Phoma vadicis-Oxycocci, P. vadicis-Andromedae, P. vadicis-Vaccintt, 
P. vadicis-Tetvalicis and P. vadicis-Ericae. 
+ M. C. Rayner, Obligate symbiosis in Calluna vulgaris. Ann. Bot. XxIx, 
PP- 97-133 (1915). 
