702 FUNGI 



at all. Some observers are of opinion that the fungus produces 

 oospores similarly to the allied species Phytophthora omnivora, 

 and that it is by means of these sexually-produced resting- 

 spores that the fungus is reproduced in summer, the resting- 

 spores having remained dormant during the preceding winter 

 in the debris of old tubers and diseased haulm : other authori- 

 ties hold that oospores are not produced by Phytophthora 

 infestans. The evidence for and against the existence of sexually- 

 produced spores is so conflicting that we consider no sound 

 conclusion can at present be drawn in favour of either 

 view. 



Phytophthora infestans attacks and destroys the leaves of 

 the tomato, petunia, bitter-sweet, and other members of the 

 Solanaceae. 



Prevention and Remedy. — (a) It is a commonly observed 

 fact that the several varieties of the potato are not all affected 

 equally by the fungus : careful endeavour should therefore be 

 made to determine which varieties are least subject to the 

 disease in years when the malady is prevalent, and those only 

 should be cultivated. As far as possible careful trial of new 

 varieties is advisable, with a view of meeting with kinds highly 

 resisiant to the disease. 



(3) Wherever feasible, collect and burn all the haulm and 

 rotten tubers from the infested crop, and never allow diseased 

 refuse to be thrown on the manure heap. This advice is based 

 on the assumption that the fungus is capable of existing in some 

 form through the winter in such refuse, and is liable to spread 

 the disease in the following summer. 



(f) Avoid using for 'seed' apparently sound tubers from a badly 

 diseased crop; for according to some authorities it is within 

 such tubers that the mycelium hibernates and spreads the 

 disease in the following summer as explained above. 



(d) ' Moulding-up ' or covering the tubers with a consider- 

 able layer of soil is said to diminish the attacks on the tubers 



