STEWART'S DISEASE OF SWEET CORN (MAIZE). 93 



Several attempts were made to inoculate sweet-eorn by puncturing the stem near the ground and 

 inserting a small quantity of the diseased tissue of an affected plant. In some of the large varieties 

 the inoculated plants remained healthy to the end of the season. In the smaller varieties the disease 

 usually appeared in from two to four weeks after inoculation, but the uninoculated plants used as a 

 check, likewise, invariably became affected to a considerable extent, so that no trustworthy informa- 

 tion could be obtained from such experiments. 



Finally it became evident that the plants must be grown in pots of sterilized soil if the inoculation 

 experiments were to furnish results of any value. A quantity of soil was thoroughly sterilized in 

 steam sterilizers and placed in large pots. On July 3 Early Cory sweet-corn (grown in Iowa) was 

 planted in the pots and inoculation experiments with pure cultures of the yellow germ were started. 

 The pots were allowed to remain uncovered [out of doors] ; otherwise, all precautions were taken to 

 prevent contamination. Nevertheless, an undoubted case of the disease was found in one of the 

 check pots on August 3, and later several others were found. This meant that diseased seed had been 

 used and the experiment was worthless except to prove that infection may be brought about by the 

 germs which cling to the seed. 



This appears to have been the only inoculation experiment attempted by Mr. Stewart 

 with pure cultures. At least it is the only one mentioned, and no statement is made as to 

 how many, if any, of the inoculated plants contracted the disease or how near these were to 

 the check plants. When the rainfall was not sufficient they were watered with sterile water. 



Three unsuccessful attempts were made to produce the disease in yellow dent field-corn by inocu- 

 lation. On August 20, 1895, ten plants of yellow dent corn (variety unknown) were inoculated by 

 puncturing the stem at the surface of the soil with a sterilized scalpel and then inserting into the punc- 

 ture a small quantity of the yellow substance taken directly from the interior of the stem of a diseased 

 sweet-corn plant. These plants were under observation until frost (about October 7), but none of 

 them showed any symptoms of the disease. On July 12, 1897, twenty plants of yellow dent corn, 

 variety Golden Dent, were inoculated in the same manner as in the experiment of 1895. None of 

 these plants developed outward symptoms of the disease, but a month after inoculation it was found 

 that in several of the plants the yellow bacillus had ascended a few of the tibro-vascular bundles, where 

 it was visible to the naked eye as far as the third node above the point of inoculation. It was notice- 

 able, however, that it occurred only in bundles which had been ruptured by the needle used in inocu- 

 lation. In 1897 a 50-foot row of the same Golden Dent corn was inoculated by placing in the drill, at 

 time of planting, a liberal quantity of soil, in which diseased plants had grown the preceding season. 

 Not a single plant developed the disease. 



Pop-corn, also, has resisted all attempts at inoculation. In 1897 a 50-foot row of pop-corn, var- 

 iety Maple Dale, was inoculated by putting diseased soil in the drill at time of planting. None of the 

 plants became diseased. On July 8, 1897, twenty plants of the same variety of pop-corn were inocu- 

 lated by puncturing the stem and inserting diseased tissue into the wound, as in the experiments with 

 sweet-corn and field-corn. None of the plants became diseased, but as in the case of field-corn the 

 germ could be seen in some of the bundles up to the third node. 



Oats, inoculated by means of diseased soils, and teosinte (Euchlaena luxurians) , inoculated both 

 by puncture and diseased soil, gave negative results. 



Stewart believed the plants became infected through their root-system. He says in so 

 many words: 



Since the cause of the disease is entirely within the tissues and probably gains entrance through 

 the subterranean parts of the plant, the application of fungicides to the parts above ground must be 

 absolutely without avail. 



Stewart observed the disease in Early Cory, Manhattan, and many different varieties 

 of sweet corn on Long Island. 



In 1897 he found it very prevalent as early as June 12, among plants which were 8 to 10 

 inches high. 



In some plants he was able by means of the microscope to demonstrate the presence of 

 the bacteria in the bundles before the yellow slime could be detected with the naked eye, and 

 before there were any outward manifestations of the disease other than dwarfing. 



In plants dead of the disease he found an abundance of bacteria in all parts of the stem 

 "up to the tassel and in the ear." It is easily demonstrable, he says, that insects are not 



