i)ec; 189'i.] 



INJURIOUS INSECTS AND FUNGI. 



207 



action of the fungus. Upon examining the potatoes when tliey 

 were dug up they were found to be perfectly free from disease, 

 but very small, and when cooked they were waxy and flavourless. 

 Later on, the tubers were examined in the clamp, and there were 

 then no traces of disease in them. 



This disease was also noticed by several observers in allotment 

 grouuds, and small gardens, where potatoes are often grown 

 repeatedly on the same plot. 



In most of the previous descriptions of this fungus, notably in 

 those of Ellis, Martin, and Saccardo, it is stated that it is found 

 on the under surface of eroded spots and faded portions of the 

 dying leaves of potato plants. It was, however, plainly seen in 

 the past season growing and active upon living potato plants 

 and most evidently deriving sustenance from them. In his 

 annual report for 1892 to the United States Department of 

 Agriculture, Mr. Galloway writes :— " Early in the season it was 

 noticed that potatoes in Maryland and elsewhere were being 

 seriously injured by a fungus attacking their leaves and causing 

 them to turn brown and dry up. The tops of nearly all the 

 early potatoes were destroyed in this way before the tubers 

 were half grown, so that the crop was much shortened. The 

 fungus causing this injury was, upon examination, found to be 

 Macrosporium solani, a form widely distributed in this country 

 upon the potato, tomato, and other plants of this family." In a 

 recent Bulletin, No. 15, of the " Farmers' " series, the chief of the 

 Division of Vegetable Pathology of the United States Depart- 

 ment of Agriculture states that Macrosporium solani attacks, 

 and destroys, the living leaves of potato plants, and that there is 

 reason to believe that " this disease is often more widespread 

 and destructive than the true blight, Phytophthora infesfans." 



In a report in 1892, Mr. Fletcher, the botanist to the Dominion 

 Experimental Farms at Ottawa, writes of the defoliation of 

 potato plants being due more to Macrosporium solani than to 

 Phytophthora infestans. Mr. Weed, of the New Hampshire 

 College of Agriculture, in his work on Fungi and Fungicides, 

 shows clearly that Macrosporium solani is not saprophytic. 

 He remarks that this disease appears early in summer in the 

 shape of small brown, brittle spots scattered over the leaf ; the 

 spots gradually enlarge, and finally run together to form brown 

 patches. The entire plant finall}^ withers and dies long before 

 the proper period, the tubers being small — generally less than 

 half full size. 



Figure 1 shows the under side of a potato leaf with the 

 fungus upon it. At first, a small greyish- brown spot is visible. 

 This extends gradually in concentric rings after the manner of 

 Macrosporia, and pieces of the leaf eventually fall out leaving 

 holes with ragged margins. 



The appearance of this fungus is quite different ',from that of 

 Phytophthora infestans. The hyphse, threadlike branches of the 

 mycelium, are brown, somewhat curved and septate, whereas 

 those of the Phytophthora are colourless and not septate. The 

 qonidia, or spores, of Macrosporium, solani are oblong, pointed, 



