S U M M A R YCephalosporium maydis infects young maize plants easily, but as plants age fewer are infected and none after approx. 50 days from sowing. The mesocotyl and seminal, fibrous and adventitious roots are attacked, especially when there is damage or much inoculum. Most penetration occurs where roots are elongating and emerge from the mesocotyl or from fibrous roots. At first the fungus grows superficially on roots, producing hyphae with short, brown, thick-walled, and swollen cells. After penetrating, the fungus spreads towards the xylem, where it grows slowly at first but after 5 weeks grows faster upwards.C. acremonium causes black-bundle disease of maize. It seems to infect plants growing in unfavourable conditions but the details remain uncertain. The percentage of plants infected was not related to the amount of inoculum and the fungus may not be a primary parasite. The sterile culture filtrate of the fungus produces vascular discoloration and wilt of maize seedlings.

The interaction between Fusarium oxysporum (cause of cotton wilt) and Cephalosporium maydis (cause of maize late-wilt) on cotton roots is associated with an appreciable decrease in the severity of the cotton wilt disease.

The competitive saprophytic ability (CSA) of Cephalasporium maydis was smaller at 30 "C when measured by the agar-plate modification than by the original Cambridge method. The agar-plate method suggested that C. maydis was a less competitive saprophyte than C. acremonium although both were low in CSA.C. acremonium grows and sporulates well on organic and synthetic media. C. maydis grows faster but is more exacting nutritionally and is less able to decompose cellulose or maize straw than C. acremonium. Neither fungus produced pectolytic culture filtrates and both were susceptible to antibiotics produced by soil micro-organisms.C. maydis survived on maize straw much longer than C. acremonium. In field soils C. maydis colonized and survived in supplemented wheat bran poorly and not below the top 20 cm of soil.

Inoculations with Corynebacterium rathayi (E. F. Sm.) Dowson, alone or combined with the eelworm Anguina tritici into the leaves and shoots of cocksfoot grass (Dactylis glomerata L.) and wheat (Triticum vulgare Vill.), fail to cause infection. Inoculations made through the soil with Corynebactmim rathuyi and C. tritici (Hutchinson) Burkh. plua Anguina tritici cause infection in wheat but not in cocksfoot grass. The symptoms produced on wheat resemble those of yellow slime disease of cocksfoot grass. Successful infection of wheat with Corynebacterium rathay. or C. tritici is dependent on the presence, in the soil surrounding the plants, of Anguina tritici together with one of these bacterial species, which are considered to be so closely related as to suggest that Corynebacterium tritici is but a geographical variety of C. rathayi.