122 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



of fimg-QS diseases that affect tlie potato in one way or another, the 

 disease most to be feared, and which has caused greater losses to this 

 crop tlian all other sources of injury combined, is the Potato-rot. 



There are very few farmers in the principal potato-growing States 

 who have not suffered to some extent at least from this evil, and in 

 seasons favorable to the development of the disease many there are 

 who have lost one-half or even their entire crop on account of it. _ 



This was one of the first plant diseases investigated by scientists 

 with a view of obtaining some efficient remedy. These investigations 

 have settled the direct cause of Potato-rot beyond question, hvd a 

 practical and efficient remedy remains yet to be discovered. Indi- 

 viduals may have secured their crops from this disease by various 

 practices, some of which may possess merits that will eventually bring 

 them into general use; but however valuable these methodb really are, 

 a prejudice exists against their general adoption which would, in 

 some degree at least, be removed if they were based on other author- 

 ity. It is the purpose of this division to institute a series of experi- 

 ments to prove to the public the real value, if any, of the treatments 

 that appear to have been successful in the hands of some cultivators 

 and to try others that may give promise of success. 



With a view of learning the experience of practical men upon mat- 

 ters pertaining to this subject, and at the same time to ascertain, as 

 far as possible, the actual range and the amount of the losses occa- 

 sioned by the disease in question, a circular of inquiry was sent to the 

 officers of all the agricultural and horticultural societies and granges 

 throughout the country, as well as to many individuals supposed or 

 known to be able to give the information desired. That nearly 2,500 

 replies, coming from every State and Territory, have already been 

 received is significant of the general interest and importance attached 

 to this subject. With the force available it is practically impossible 

 to compile and arra^nge the material thus accumulated for publication 

 in this report; but this work will be done as soon as the facilities at 

 command will permit, and the results, together with a more complete 

 account of the nature and habits of the fungus that produces the dis- 

 ease, will appear in a special bulletin of the division. 



This report is limited to the following brief account of Ihe disease, 

 prepared by my assistant, Mr. Erwin F. Smith, who has also ren- 

 dered valuable assistance in preparing other parts of this report. 



Numerous fungi are found upon the potato, but Phytoplithora 

 infestans De Bary appears to be the most widely destructive one. 

 Many of the others are only such as feed upon vegetable matter 

 already in part or wholly disorganized. This seems to be the case 

 with most of the bacteria and with all of the various molds which 

 abound in rotting potatoes, though not more than in other decaying 

 substances. A common ascomycetous fungus, one form of which is 

 known a.s Fusisporiuin solani Mart., has been described &?, xjarasitic, 

 and stated to be "sometimes equally damaging to potatoes with the 

 Peronosjjora [Fhytophthora] itself," but of this there is no good 

 evidence. Phyto})lifliora infestans is exclusively parasitic, though 

 not entirely confined to the potato. The external appearance of this 

 fungus is shown in Plate VII. 



The brown or black discoloration of the tubers and the blight of the 

 leaves have been thought by muny gi'owers to be different diseases, 

 but they are only two phases of one disease, being due to the same 

 fungus. During the growing season the mycelium of the Fhytoph- 

 thora may be found in the diseased stems and leaves; and, if there be 



