CONTENTS. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



VIII. 



I 



PAOB 

 Introduction, .......... 99 



Germination of the spores, ........ 100 



Review of the literature on essential conditions for smut sporo 



germination, ......... 100 



Essential conditions for germination of Urocystis crpulac spores, . 104 



The process of germination, ....... 108 



Comparison with the germination process in other species of Uro- 

 cystis, . . . . . . . . . . 110 



Comparison with the process as described by Thaxter, . . Ill 



Saprophytism, . . . . . . . . . .112 



Isolation, .......... 112 



Cultural characters, . . . . . . . .112 



Effect of freezing the cultures, . . .115 



Microscopic characters of the mycelium in culture, . . .115 



Fate and function of the detached hyphal cells, . . .116 



Life in the soil, . . . . . . . .117 



Summary of the saprophytic stage m the natural life history, . 117 



Infection, ........... 118 



Development of the onion seedling, . . . . .118 



Period of susceptibility, ....... 120 



Point of infection, ........ 122 



Character of the inoculum, ....... 123 



Method of entrance, ........ 123 



Passage through the epidermal cell.s, ..... 124 



Multiple infection, ........ 125 



Incubation period, ......... 125 



Young hyphse in the intercellular spaces, .... 125 



Haustoria, .......... 126 



Absorptive hyphal expansions, ...... 127 



Progressive infection of new leaves, ..... 128 



Sporogenesis, .......... 128 



Summary, . . . . . . . . . . .131 



Litarature cited, .......... 132 





