206 PROCEEDINGS OF THE 



will yet grow up in a mischievous crop. On the other hand, if he 

 allows these decaying haulms to lie about his fields, the oospores 

 will be washed into the soil and into ditches and drains, and 

 moisture is especially favourable to the preservation and germina- 

 tion of the fungus. Destruction by fire seems to be the proper 

 course to pursue with potato refuse, but it remains a question how 

 much effect that might have after all on the disease. 



The modes of reproduction in the fungi are very intricate and 

 varied, but, so far as the question of their parasitism or saprophytism 

 is concerned, it is unnecessary to enter further into details. It 

 will be sufficient to indicate wherein these plants are especially 

 adapted in their reproduction and growth for a parasitical or 

 saprophytical way of life. 



(1) The minuteness of the spores renders them easily carried 

 about in the atmosphere, &c. The size of these spores varies 

 considerably from a microscopic point of view; but all are 

 exceedingly minute in the ordinary acceptation of the term . The 

 spores of common "corn-smut" (Ustilago segetum) for instance, are 

 so very minute that 49 of them would be contained in the 

 T6-o"^ooo tn P art °f a sc l uare inch, or nearly 8,000,000 to the square 

 inch. It would take millions of the spores of moulds to form a 

 body the size of a pin-head. 



(2) The myriads of spores produced are an important element in 

 ensuring extensive di fusion, so that they may find a suitable nidus. 

 To give some idea of the number of spores produced in an in- 

 dividual fungus, it has been calculated that in a specimen of 

 Boletus subtomentosus five inches in diameter, there were produced 

 no less than 5,000,000,000 spores. 



(3) The exceeding rapidity of their growth, which is largely 

 dependent on their modes of nutrition on organic matter, is evidently 

 of advantage in connection with their parasitism and saprophytism. 

 The Great Puff ball will grow to the size of a child's head in a few 

 hours, and Dr. Lindley computed that its cells multiply at the rate 

 of 60,000,000 in a minute. Dr. Carpenter gives an instance of 

 the rapid growth of Toadstools, as indicated by their expansive 

 power in lifting some of the heaviest stones of a pavement com- 

 pletely out of their beds, one of these stones weighing 83 lbs., 

 and the resistance offered by the mortar having also to be taken 

 into consideration. The rapid development of Peronospora 

 infestans has already been referred to. 



