76 PROTISTS AND DISEASE 



pause is required between the formation of zoospores in 

 two separate sporangia and their discharge. The conjuga- 

 tion is selective isogamy, the chief details of which are shown 

 in Fig. 22, which also shows the relation of the parasite to 

 the host-cell, and its development to a chromidial resting- 

 cell or sporangium in which zoospores are formed. 



Miss Curtis found that the maturation-period of the 

 resting- sporangium from the time of the formation of the 

 outer membrane was 2| months. Rain-water produced the 

 quickest germination. A very significant point regarding 

 the maturation of the resting sporangium of 8. endobioticum 

 is mentioned. E. S. Salmon (1908) as the result of a series 

 of infection experiments concluded that resting sporangia, 

 after exposure for 1| hours to a temperature ranging from 

 5 C. to 6 C., could dispense with the winter dormancy 

 and germinate at once. In Nature the sporangia ripen in 

 the host-tissue ; when this decays they are liberated. 



Shortly before maturation the sporangium enlarges 

 rapidly, sometimes doubling its diameter. At this stage 

 the two outer membranes are soft and the innermost is 

 hyaline. This distention gives the zoospores more room 

 and their flagella attain their full length. Rupture of the 

 sporangium is by a slit. The zoospores are in active move- 

 ment before the rupture, and at suitable temperatures, 

 12 C. to 14 C., continue to move for 2 hours. Zoospores 

 from resting sporangia measure 2/x, one-third larger than 

 those from the sorus. 



