STEWART'S DISEASE OF SWEET CORN (MAIZE). 125 



present, but not alive after so many months. Several kinds of yellow bacteria were obtained 

 in abundance from the numerous poured-plates, but none corresponded exactly to Bacterium 

 stewarti. Many resembled it in the agar-poured-plates, but all of the hundred or more 

 colonies selected as hopeful differed in some particular, i. e., either they grew differently 

 on potato, or coagulated milk, or liquefied gelatin, or clouded Cohn's solution, or refused 

 to grow in Uschinsky's solution, or formed gas, or rapidly reddened or blued litmus milk, 

 etc. They were checked up against three strains of Bacterium stewarti obtained from as 

 many different localities. One form in particular, designated as "N l( " which appeared as 

 though it might be Bacterium stewarti (before additional cultural tests were made which 

 threw it out) was pricked into the leaves of young plants of this variety of sweet-corn 

 copiously, but no disease resulted.* 



This failure to obtain Bacterium stewarti believed to be present on the kernels is prob- 

 ably to be attributed to the presence in abundance of non-parasitic yellow bacteria on the 

 surface of the corn, while the right organism occurred in a viable form in very small numbers 

 or not at all, so that on the poured-plates it either did not appear or occurred in such 

 small numbers as to be overlooked, the problem of finding it on agar-poured-plates under 

 such conditions being a difficult one. Probably if we had cultured from crushed kernels 

 we would have obtained the organism. This conclusion is borne out by the following 



experiments. 



SERIES XVI TO XIX. 1908. 



On July 23, 1908, a center bed extending the whole length of one of our large hot-houses 

 was planted to this corn. Hitherto corn had never been planted in this house. Orange 

 trees of large size stood in this earth and had done so for many years. The trees were 

 grubbed out, the soil was spaded, a little bone meal was added, and then the suspected 

 corn was planted thickly in rows crosswise of the bed, at a distance apart of about 18 inches. 

 The bed was divided crosswise into four portions as follows: (1,2) two plots planted with 

 selected sterilized seed; (3) one plot planted with untreated seed just as it came from the 

 original sack ; (4) one plot planted with the most inferior looking kernels in the sack (also 

 untreated). 



The crop was harvested on October 6 to 9. Cross-sections of every stem were examined 

 under the hand-lens by the writer. Some were also examined under the compound micro- 

 scope and many were put into alcohol for future use. The results were as follows: 



(1) Selected (hand-picked) good-looking seed, soaked 15 minutes in 1:1000 mercuric chloride 

 water, rinsed in tap-water, and immediately planted (i i rows) : 



Number of healthy plants, 1,090; number of diseased plants, 13. 

 Total, 1,103; per cent diseased, 1.2. 



Remarks. None of the affected plants were badly diseased. The record is as follows: Eleven 

 slightly diseased, 2 of which had open wounds on the stem above. Only one bundle visibly infected 

 in most of these. Bacteria visible only in the basal part of the stem. The twelfth had 3 diseased 

 bundles, and the thirteenth, which contained several bundles occupied by yellow bacteria, had one 

 whole internode above soft-decayed. Possibly those with bruised or wounded stems should have 

 been omitted from the record. None had yet reached the stage of shriveling leaves. 



(2) Selected (hand-picked) good-looking seed, soaked 10 minutes in i : 1000 mercuric chloride 

 water, rinsed in tap-water, and immediately planted (12 rows): 



Number of healthy plants, 1,277; number of diseased plants, 23. 

 Total, 1,300; per cent diseased, 1.8. 



Remarks. Two plants with 3 bundles infected; 19 slightly diseased (a few bundles in the lower 

 part of the stem) ; 2 badly diseased, both having many bundles occupied by the organism and the 

 leaves dried out. In one, the stem was infected the whole length, and toward the base nearly every 

 bundle was occupied by the yellow slime. 



*In 1904, Miss Florence Hedges, of my laboratory, obtained similar negative results on a much larger scale, 

 using a yellow organism supposed at first to be Bact. stewarti, but afterwards found to behave differently on certain 

 media. Three hundred sweet-corn plants were inoculated very thoroughly on the leaf tips when the seedlings were 

 extruding water, but no disease resulted. 



