268 BACTERIA IN RELATION TO PLANT DISEASES. 



dissolved in sterile water and fed into the vascular system of the stem of a healthy plant causes wilt 

 in course of a few days if used unboiled, but not if boiled. Much difficulty was experienced in keeping 

 cultures alive throughout the year. It was accomplished only by repeated transfers and storage at 

 20 C., and then they were found to have lost much of their former virulence, but this was restored 

 by passage through a fresh series of plants, but not the pigment production. Solution of the middle 

 lamella and disintegration of the tissues by separation of the cells is a noticeable feature in this 

 disease. The formation of the brown pigment in cultures tends to destroy their virulence. " It was 

 found that when the cultures reached this stage they were no longer pathogenic, and in fact in many 

 cases failed to produce growth when transferred to similar media." [See footnote page 232.] 



This interesting paper raises the question whether in some of the preceding studies 

 two organisms may not have been confused, i. e., a non-motile, black-pigment-forming 

 species (the true pathogen) and a closely associated non-pathogenic, motile species pro- 

 ducing only a yellowish growth on media. Certainly the writer of this monograph 

 often has failed to observe motility, has frequently seen only a yellowish-brown stain in 

 potato cultures (and these usually are non-pathogenic), and has seen more variations in 

 virulence and had more failures in the way of inoculations than with almost any other 

 organism worked with. 



As soon as possible therefore after reading Hutchinson's paper additional obser- 

 vations and experiments were made to determine whether the pathogen is motile or non- 

 motile. For this purpose we used cultures of the tobacco organism received from Honing 

 (the only living cultures of this species then in the laboratory). 



These studies confirmed earlier ones made on the North American organism. The 

 organism examined on the margin of hanging drops was clearly motile, sometimes darting 

 entirely out of the field, and Miss Bryan succeeded in demonstrating polar flagella by means 

 of stains. The actual agar-streak culture which yielded the polar flagella (fig. 1340) was then 

 used for successful inoculations on tobacco (fig. I34&). If the streak was a pure culture, 

 then there can be no question as to the motility of the parasite. It was a subculture from 

 the third sending of Honing which we designated as Medan III. I do not know its history 

 on the other side, but we may suppose that it was the product of a single colony ; it 

 certainly behaved in various media (potato, agar, milk, etc.) like a pure culture. We also 

 plated it out on agar and observed no contaminating organisms. The streak used for the 

 flagella staining was not started, however, from a single colony. For this reason the work 

 was done over using subcultures from single colonies with the same results (see p. 265). 



THE SOUTH AFRICAN DISEASE. 



In 1906 Mr. C. P. Lounsbury reported on a serious tobacco wilt occurring in South- 

 eastern Cape of Good Hope, South Africa. This paper is a summary of investigations 

 carried on in 1905-6 in regard to "serious and extensive losses in the tobacco fields of the 

 Kat River Valley." A farmer at Balfour describes the disease as "a plague which is devas- 

 tating the tobacco of almost the whole district." Reports of W. R. Dewar, Entomologist 

 of the Eastern Province, Mr. Thomas Bowhill, the Veterinary Bacteriologist, and Mr. 

 Lounsbury constitute the body of the text, together with several excerpts from letters of 

 others as to the cause or signs of the disease. 



Mr. Dewar's description of the disease is as follows : 



The farmer can see a plant just beginning to wilt when he is two or three rows away. It is not 

 so noticeable to a casual observer; but, upon closer examination, the farmer is generally correct. A 

 slight wilting is noticeable, which can not be distinguished in healthy plants. As the disease con- 

 tinues, the plant wilts more, the leaves droop considerably, turn yellowish or sickly, and eventually 

 the plant dies. In many cases when a plant is in the advanced stage the roots are soft and black. 

 This has led the growers to say that the disease is in the soil. Sometimes only half or one side of a 

 plant seems affected, and in some cases only one side of one or two leaves on a plant. In many cases 

 I noticed that the stalk had become black and dry in longitudinal wavy lines under the cortex, and 

 that the drying had pulled the cortex down so as to form irregular corrugations. 



