W. MCRAE 



245 



be found, but as a rule though it is sometimes irregularly swollen, it does 

 not differ from one that has passed through a cell. 



The reproductive organs of this Phytophthora are of two types, sporangia 

 and oogonia. The former are found on the hyphse that protrude above the 

 surface of the plant and the culture medium, while the latter are embedded 

 in the tissues of the plant and within the culture medium. 



Sporangia are borne both terminally and laterally on aerial hyphae both 

 in culture and in nature, and on hyphae lying along the surface in culture, and 

 are formed abundantly in suitable conditions. When aerial hyphae from a 

 vigorously growing culture or from the surface of a plant are placed in water — 

 either distilled, rain, or well-water — they form sporangia which become fully 

 formed and discharge zoospores in from twelve to twenty-four hours. As an 

 example a slightly infected fruit was placed in a moist chamber at 5 p.m. 

 Next morning at 8 a.m. a few aerial hyphae were removed and placed in sterile 

 rain-water under a cover-slip. A drawing of one branchlet having young 

 sporangia was made and measurements were taken by 8'30 a.m. (Pit. II, 

 figs. 22 — 25). Six young sporangia (Nos. 1 to (3) were measured ; une 

 (No. 7) was a minute swelling at the end of its hypha ; another (No. 8) was 

 seen as a small swelling 10;t;t in diameter at 9'30 a.m. The succeeding 

 measmements are given in the table below. The slide was several times 

 irrigated during the day. Between 3 and 4 p.m. five sporangia discharged, and 

 one had produced a germ-tube 57m long. Two failed to discharge by 5 p.m. 

 when the hypha was washed away and lost. 



Similar results are got when a minute culture on the underside of a cover- 

 sUp on a Ward's tube is placed in a drop of water on a shde. In a moist 

 atmosphere or in a small quantity of still water mature sporangia remain 

 ready to discharge for a considerable time, but when irrigated or placed in a 

 large drop of water they discharge in from 10 minutes to half an hour. In 

 culture they discharge in the moiatuie of condensation on the j'urface of the 



