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.

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.

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.

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.