94 BACTERIA IN RELATION TO PLANT DISEASES. 



responsible for the disease. Stewart also makes the following interesting observations on 

 the relation of weather to the progress of the disease : 



If plants are examined in periods of wet weather it will be found that the amount of the yellow 

 substance which they may contain in their vessels without showing outward symptoms of the disease 

 is much greater than it is in dry weather. * * It is interesting to observe the effect of alternat- 



ing periods of wet and dry weather. For about one month preceding July 12, 1897, it was very dry 

 on Long Island so dry that in the latter part of the period some crops suffered severely. During 

 this time the corn disease was very destructive. Then came about three weeks of rainy weather fol- 

 lowed by a short period of dry weather. Many plants which were partially dead revived during 

 the rainy season and promised to outgrow the disease, but as soon as the rains ceased they suddenly 

 collapsed. 



In 1898, as a result of observations in Michigan, I pointed out the extreme probablity 

 of the bulk of the infections taking place not through the roots but in the seedling stage of 

 the plant through the water-pores. Thereafter I contented myself with a study of the cul- 

 tural characteristics of the organism which had been sent to me by Mr. Stewart for that pur- 

 pose, hoping the latter would go on and complete the gaps in his infection experiments. 

 This he did not do. In 1902, therefore, having an opportunity to study the disease on Long 

 Island, the writer renewed his cultures and afterwards inoculated many plants in the city of 

 Washington, where the disease was not then known to occur naturally. The results of these 

 inoculations were very convincing, but before proceeding to an examination of them the 

 reader will be interested in some statements regarding the origin of the cultures used for 

 making these inoculations. 



FIELD OBSERVATION IN 1902. 



My observations on Long Island are recorded in the following transcript from a note 

 book: 



Notes of July 16, 1902, on Stewart's Sweet Corn Disease. 



Found disease at William M. Croucher's place, on the Merrick Road, 1.25 miles from Jamaica, 

 Long Island, New York. The disease occurred on a good quality of truck-land, loamy and not 

 wet. This land rents for $10 per acre per year. Nothing in the surroundings to explain the appear- 

 ance of the disease. Mr. Croucher, who is perhaps 30 years old and has been a trucker all his life, 

 says he has seen the disease ever since he can remember. He says some varieties of sweet corn are 

 much more subject to it than others. The Early Cory is one of the sorts most subject. His field of 

 about 3 acres was in good condition as to cultivation. The plants were tasseling in part. The field 

 was not badly diseased. He had already pulled out some of the diseased stalks, and I found 15 or 20 

 more. So far as I can judge, the disease is to be told by the shriveling of the leaves and by the pre- 

 mature blossoming of the male flowers. At some distance the male flowers on the diseased plants 

 looked white and dry. Those on the healthy plants were green or purplish. Every plant of this sort, 

 namely, with white and dry spikelets and shriveling leaves, proved on cutting open to be full of bac- 

 teria, although the stems were green and sound externally and in most cases all the bases of the leaves. 

 The plants were also well provided with roots. As a rule such plants were somewhat dwarfed. 



I was surprised at the complete occupation of the vascular system the whole length of the stem 

 except in the extreme top. A cut anywhere else across the stem was followed by a yellow ooze from 

 the vessels even as far up as a foot ifrom the top, and undoubtedly the organism could have been 

 detected still farther up with the aid of the compound microscope. The ooze from the bundles was 

 yellow, especially in the lower part of the stem, e.g., one foot from the ground. In the upper part of 

 the stems it was usually very pale. This I interpret to mean not two organisms, but two stages of 

 one, the lower down, yellower ooze consisting of older organisms and growing perhaps in the presence 

 of a greater amount of air. (See p. 58, and also Yellow Disease of Hyacinths, vol. II, p. 345.) 



Infection by boring or gnawing insects was out of the question in case of these plants. The 

 surface was smooth and unbroken. There were no insect injuries and no ooze of the bacteria to the 

 surface. Except in the extreme base of the stem (of which more later) the bacteria appeared to be 

 confined quite strictly to the bundles. The tissue between was sound, that is, normal in color and 

 free from any appearance of disease. The bacteria were not only very abundant in the bundles of 

 the stem, but were also in the green bases of many of the shriveled leaves. 



Whether these leaves were infected from below (from the stem) or from above (through their 

 water pores or stomata) could not be determined by a field examination. Tips of many of the shriveled 



