DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 543 



The germ tube of the swarm spores penetrate the tuber, as easily 

 as the leaf, if they happen to be washed down to the soil. Recently 

 G. P. Clinton^ has discovered the oogonia, antheridia and oospores of 

 Fhytophthora infestans after they had been sought for by mycologists 

 since 1845, and thus an American mycologist has added one more 

 achievement to the list of important work accomplished by American 

 scientific men. 



Spraying the foliage with Bordeaux mixture (5-5-50) has proved 

 an almost complete remedy against both the Fhytophthora blight and 

 the rot, and also operates benefi^cially to the potato plant in other ways. 

 Burying the tubers to a sufficient depth (about 4 to 5 inches) has been 

 found beneficial, as also the disinfection of the tubers designed for seed 

 purposes by exposure to dry heat 4o°C. (io4°F.) for four hours. Tuber 

 infection may be prevented by spraying the soil, even when the fungus 

 is allowed to develop unchecked on the foliage. When the tops are 

 attacked by late-blight, the harvesting of the tubers should be delayed 

 until a week or more after the death of the tops. Longer delay does no 

 harm, unless the season be wet and the soil exceptionally heavy. Dry 

 cool storage is of primary importance, the use of lime, or formalin, for 

 disinfection being valueless.^ It seems from investigations, that have 

 been made, that well-marked and fixed differences exist among potato 

 varieties in relative susceptibiUty to invasion by the late-blight fungus, 

 in other words, in disease resistance. 



Powdering Dry-rot {Fusarium trichothecioides Wollenw.). — This 

 fungus kept in artificial culture has been used successfully in the artifi- 

 cial inoculation of potato tubers, as laboratory exercise with univer- 

 sity students in mycology. In every case, the rot has been secured and 

 the students have imbedded pieces of tuber and fungus in paraffin; 

 cut the same with a rotary microtome and mounted and stained the 

 sections for microscopic study. 



Fusarium trichothecioides forms two kinds of conidiospores : (i) The 

 comma type, formed as a slightly curved comma ellipsoidally rounded 

 on both sides; and (2) the normal macroconidiospores. The plecten- 



1 Clinton, G. P.: Oospores of Potato Blight. Report of the Connecticut 

 Agricultural Experiment Station, 1909-1910: 753-774 with 3 plates. 



2 Jones, L. R., Giddings, N. J. and Luxman, B. F.: Investigations of the Potato 

 Fungus, Fhytophthora infestans. Bull. 245 U. S. Bureau of Plant Industry, 

 1912, with full bibliography; Melhus, I. E., Hibernation of Phytophthora infestans 

 of the Irish Potato. Journ. Agric. Research V: 71-102. 



