Puccinia malvacearum in monosporidial culture

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1. A method of monosporidial infection for the rust fungi has been perfected with the help of the micromanipulator. 2. By this means Puccinia Malvacearum has been proved to be homothallic. 3. The effect of high atmospheric humidity was to increase the tendency to Sclerotium formation and to diminish the tendency to sporulation. A similar effect produced by absence of light was indicated. 4. The period required for development of both monosporidial and mass inoculations has been found to vary inversely with the temperature. 5. Shortly after formation and sometimes even before abstriction the sporidium becomes binucleate. 6. Entry to the host cell is effected through the epidermis by the formation of a fine penetration hypha at the tip of a short germ tube. 7. The contents of the sporidium pass through this to form an infection vesicle, an aseptate binucleate hypha, and the primary infection hypha. 8. This primary infection hypha is wide, and becomes septate forming three or four uninucleate cells. 9. After septation each of these cells puts out a thinner hypha which is the beginning of the vegetative mycelium. The vegetative mycelium is both intracellular and intercellular with haustoria in all tissues. 10. The development continues until the lower epidermis is reached. 11. A renewed vigorous growth starts from the centre of the mass of vegetative mycelium. Branches are put out, these ramify repeatedly towards the lower surface. 12. These branches are wider than the early vegetative mycelium and form club-shaped end cells which, however, are still uninucleate. 13. The change to the diplophase is now effected and evidence is cited for the occurrence of this both by nuclear migration and nuclear division not accompanied by wall formation. 14. That the diplophase arises more than once in one sorus is evidenced by the irregular distribution of uninucleate and binucleate cells. 15. Each binucleate cell divides into a lower stalk cell, and an upper cell, which by a further division forms the two-celled teleuto-spore. 16. The epidermis is ruptured and the teleutospores can germinate immediately they are exposed provided moisture is available. 17. In a moist atmosphere germination takes place to give a curved promycelium and sporidia : in a water film the promycelium is straight and abstricts conidia. 18. The conidia may develop further to give sporidia. 19. The return to the haplophase occurs in the promycelium. 20. There is no biological difference between the teleutospores formed in different seasons. 21. During winter the life cycle is retarded by the less frequent occurrence of conditions favourable for the germination of the teleutospores. 22. New infections occur throughout the winter so that all the pustules present in the spring are not the result of a late autumn infection.