Early Blight of the Potato. 4!67 



and thorongh tillage. Another evident precaution is to destroy all the 

 diseased plants, so that the fungus ma}- not be allowed unchecked to 

 propagate itself and sow its reproductive bodies in the soil. 



There is yet another remedy to be mentioned, which has been 

 extensively employed in the United States, where the disease seems 

 to be worse than in other countries, and that is the use of the well- 

 known fungicide, Bordeaux mixture. The orchardist has to spray his 

 apple and pear trees for black spot if he wishes to save his crop from 

 being ruined in a spotty season, and the potato-grower seriously 

 threatened by the Early Blight, will find it to his advantage to spray 

 likewise. If spraying is to have its full effect, it must be done early, 

 for in diseases of this nature, he must anticipate the attack, and not 

 wait until he sees the plants succumbing to the disease. Since, no 

 doubt, the conidia are in the soil, and attack the plant early, it would 

 be advantageous to treat the soil immediately before planting, and 

 when the plants are about six inches high. The formula known 

 as 6.4.40 or 6.4.50, may be recommended, and it has been found that 

 spraying at the rate of 100 gallons per acre, gave better results than 

 50 gallons per acre. 



Explanation of Plates. 



{Alteniaria solum.) 



1. Young leaf of potato affected by the Early Blight, showing the formation of 

 small discoloured spots. (Nat. size). 



2. Mature leaf of potato, showing large dry spots due to the growth of the fungus. 

 (Nat. size). 



Conidiophores and conidia of the fungus growing on the leaf, as seen under the 

 microscope, when magnified 100 diameters. 



4, 5, 6. Conidia with one, two, and three beaks, (x 250). 



7. Conidium with one beak, upon which a cup-shaped conidiophore has been 

 formed, the conidium shown in fig. 4 having fallen from it. From a culture on potata 

 leaf decoction. 



8. Chain of two conidia, in the larger the single terminal beak has become modified 

 so as to serve as a conidiophore, being terminated by the characteristic cup-shaped 

 apex. From a culture on potato-leaf decoction. 



9. Conidium showing the modification of the single terminal beak into a 

 conidiophore, with the cup-shaped apex. From a culture on potato-leaf decoction. 



10. Conidium germinating in decoction of potato leaf, showing the formation of 

 mycelium, in turn giving rise to a conidiophore and conidium. 



11. Conidia germinating in decoction of potato leaf, one of them producing two 

 coniodiophores, each bearing a conidium with two beaks. 



12. Conidium germinating in potato-leaf decoction, a secondary conidium being 

 formed at the apex of the conidiophore arising from the terminal beak. 



Note. — Figs. 1 and 2 natural size, Fig. 3 magnified 100 diameters, and all others 

 magnified 2-50 diameters. All figures reproduced from original photographs and 

 photomicrographs, by G. H. Robinson. 



