210 THE ROYAL SOCIETY OF CANADA 



10. The infecting hypha growing beneath the epidermal cells and sending a 

 haustorium into one of these cells. 



11. The formation of an appressorium above a stoma, the germ tube continuing 

 to grow without entering the stoma. 



PLATE V 



Development of Puccinia Graminis Tritici within the Tissues of a Sus- 

 ceptible Host (Marquis Wheat) 



(Continued from Plate IV). 



12. 13, 14. Hyphae sending haustoria into the host cells. 



15. A host cell containing two haustoria, one of which is clasping the cell 

 nucleus (nuc). 



16. Longitudinal section of a leaf showing the distributive hyphae running 

 between the ceils. 



17. Mycelium branching between the host cells, one fungus cell showing three 

 nuclei. 



18. Hyphae running beneath the epidermal cells. 



PLATE VI 



Development of Puccinia graminis tritici (Form XVII) on Mindum, a Susceptible 

 Host (1, 2) and on Kanred, a Resistant Host (3 to 8) 



1 and 2. Surface view of Mindum (very susceptible) showing germ tubes 

 passing near to or directly over stomata without entering. 



3. Surface view of Kanred (very resistant). Urediniospore germinating and 

 forming appressorium over stoma. 



4. Appressoria formed by 3 spores crowded together at a single stoma. 



5. Longitudinal section of leaf showing appressorium above stoma. Appres- 

 soria frequently fail to penetrate stomatal slit with peg-like process to form sub- 

 stomatal vesicle. 



6. Sub-stomatal vesicle. 



7. Six days after inoculation. Part of sub-stomatal vesicle still visible. In- 

 fecting hypha and host cell disintegrating, the former having died apparently almost 

 as soon as the latter. Hypha granular and without nuclei. 



8. Six days after inoculation. Both appressorium and sub-stomatal vesicle 

 still visible. Nucleus of hypha still clearly seen. Protoplast shrunken and rapidly 

 disintegrating. 



