I. The black lines formed by Xylaria
polymorpha (Pers.) Grey. in hardwoods.
[From THE ANNALS OF APPLIED BIOLOGY, VoL. XX, No. 1,
pp. 123 -145, FEBRUARY, 1933.]II . The black lines formed by Armillaria
mellea (Vahl) Quel.The two papers presented in this thesis deal
chiefly with a single type of zone line, namely, the
rind of a pseudosclerotium buried in the tissues of
the host. Although this is the commonest kind of
zone line, there are several other types of zone line
about which very little is known. A. brief outline
of these lines has already been given on page 126 of
the Xylaria paper, One such line is formed by the
deposition of "wound gum" as in the attack by Fom.es
applanatus on beech, while another is formed by
antagonistic mycelia on the same substratum as has
been described by Weir (2) in the case of F F. pinicola
and F. fomentarius in birch. This latter phenomenon
has also been described as being produced by strains
of myxobacteria when colonised some little distance
apart on agar (1). The writer has in his possession
a zone line reputed to be formed between the rots of
Polyporus adustus and F. igniarius but proof of this
must await further investigation. Indeed, one of the
difficulties of research on zone lines has been the
necessity for working out the whole biology of the
organisms concerned,as the zone lines, although often
a matter for comment, have seldom been investigated.Mary accounts of zone- producing fungi even omit to
mention the presence of zone lines in the substratum.
Thus before any decision as to the nature of the zone
line can be made it is generally necessary to make
a complete investigation of the fungus suspected
of forming it.This explanation of the zone line as the
bounding layer of a peeudosolerotium in the substratum
is one which may come to be applied to a large number
of fungi. For example, it may be suggested that the
black
transverse /lines on leaves attacked by Lophodermium
pinastri are of such a nature, while it can readily
be shown by inoculation that Sclerotinia fructigena
will form black zones in apples. The writer believes
that it will be possible to demonstrate all stages
between the true scierotium, the pseudosclerotium
buried in the substratum and the case where part of
the host, such as the fruit, forms in effect a
sc lerotium for the attacking fungus. Indeed, this
study of zone lines is only beginning to uncover
facts which may throw more light on the physiology
of the fungi and their methods of reproduction
