120 POTATO DISEASE. 



field of the miscroscope ; they were not outside the potato leaves, 

 but within the tissues, and they appeared as in the engraving C." 



Many of the small bodies had a still smaller one attached to 

 them, as seen in the same. They might have been easily over- 

 looked, as they were transparent and exactly the same in size 

 with the constitutent cells of the leaf.* Now our engraving of 

 the potato disease was really taken from the fruit of a diseased 

 tomato, and in the paper from which we have quoted are two 

 engravings, one of the Perospora infestans (A.B.C.) and another 

 of Fusisporium Salain (D.E.F.), but curiously enough in our own 

 engraving these two are represented as growing together. A 

 study, then, of our engraving will show the nature of two forms 

 of fungus with which the potato is affected, and from it we learn 

 that potatoes and tomatoes are liable to the attacks of two forms 

 of mildew, both of which are remarkable for the quickness with 

 which they spread and the thorough disorganization of the 

 tissues they attack. "The reproductive power of the potato 

 fungus," says Mr. Smith, " is almost unparalleled. The seed- 

 like bodies it produces are innumerable, and all these bodies are 

 again capable of increasing themselves ten-fold ; added to this 

 any detached atom of the parasite is able to continue growth, 

 and rapidly makes a new and perfect individual, this individual 

 being the predestined mother of a limitless family." 



Now the real nature of the potato murrain is better known, it 

 is presumed that it will be far more easy to cope with it. From 

 all that we have observed upon the nature of the potato fungus, 

 coupled with such descriptions as have been so well published by 

 Mr. Smith, it may be concluded that the resting spores are 

 generated in the leaves, stem, and tubers of the plant, ready to 

 spread disease throughout whole acres of the crop when the 

 climatical circumstances favour their development. As these 

 conditions prevail to the fullest extent a period of wet muggy 

 days, when there is the smallest amount of sunshine, and at this 

 season oftener than not sets in about August, when the disease 

 attacks the unripe late sorts, it is proposed to pay more atten- 



*Scionce for All, part 31, p. 215 and 216. 



