Recent Work on E?idotrophic Mycorhiza. 173 
as expressions of the diverse ways by which a compromise has been 
attained by different plants when confronted with similar problems. 
The work of Stahl has already been mentioned (p. 163). Some 
comment is required on the want of agreement between the 
conclusions reached by this author with regard to the behaviour 
and significance of the endophyte in Ericaceae and those of Rayner 
in the paper on Calluna reviewed here. Stahl’s conclusions as to 
the role of the fungus in mycorhiza were based largely on com¬ 
parative cultures of mycorhiza plants grown in untreated soil and 
in soil which had been ‘ sterilized ’ by heat or ether vapour. Having 
described experiments in which seeds of Vaccinium, sown in May 
in ‘ sterilized ’ soil, germinated without difficulty and produced 
well-rooted seedlings, which, in October of the same year were 
“ vollig pilzfrei,” he thus summarizes his conclusions regarding 
Ericaceae: 
“ Wahrend manche obligaten Mycorrhizenpflanzen, wie wir 
fruher gesehen haben, der Anzucht aus Samen und der Kultur 
grosse Schwierigkeiten bereiten, lassen sich die Ericaceen auch 
ohne Gegenwart von Wurzelpiiz unschwer kultivieren und ihre 
Samen gehen, zwar oft langsam, aber in grossem Procentsatz und 
sicher ohne Mitwirkung symbiotischer Pilze auf ” ( loc. cit.). 
Since seedlings six months old were “ pilzfyei,” the seeds from 
which they emerged must also have been free from the fungus. 
This involves recognition of a mode of infection in Vaccinium 
very different from that which takes place in Calluna and—since 
well-rooted seedlings were grown without infection of the roots— 
the absence of an obligate relation determining the formation of 
roots. The observations of Rayner on Calluna record an invariable 
infection of the seedling from the testa of the seed with subsequent 
development of root. Failing such infection, roots are not formed 
and the seedlings perish. This author also records ovarial infection 
for species of Vaccinium. It is true that experimental proof has 
not yet been offered that the course of events is similar in 
Vaccinium or that root-formation is dependent upon infection at a 
critical stage in the development of the seedling. The occurrence 
of ovarial infection in the genus, however, points to a similar habit 
in this respect, and the presence of hyphae in the ovary presumably 
involves infection of the seed-coats as the seeds mature. 
This recent work on Ericaceae certainly casts doubt on the 
experimental results claimed by Stahl and renders it necessary to 
demonstrate the practicability of raising ‘fungus-free’ seedlings of 
Vaccinium under rigidly aseptic conditions. The increased growth 
