210 BACTERIA IN RELATION TO PLANT DISEASES. 



In another series of experiments the young plant was placed in the earth and when growing 

 rapidly was watered daily with water containing a pure culture of Bad. solanacearum. No infection 

 took place. In a similar experiment, varied only in that the roots were purposely injured, the plants 

 became infected after 1 1 days with typical signs and a microscopic examination showed the presence 

 of the bacteria in the tissues, vessels included. 



In a third experiment a number of leaves of two tomato-plants were plunged into infected water 

 for some days to see if the bacteria would enter through the water-pores. After 3 days the leaves were 

 investigated microscopically. They were not infected and the writer draws the conclusion that they 

 can not be infected in this way, but this seems not strictly warranted, because of an additional state- 

 ment: "Certainly I found rather commonly Bacillus solanacearum in the large, intercellular spaces 

 under the water-pores, but not at all in the corresponding water-vessels." 



A similar result would not be uncommon at the end of 3 days in case of the cabbage infected 

 through the water-pores by Bacterium campestre, but a like conclusion would be erroneous, and it 

 seems not unreasonable to suppose in this case that after a longer period had elapsed, say 9 days or 1 2 

 days, Dr. Hunger might have obtained different results and come to an entirely different conclusion, 

 since in the cabbage after that time the bacteria would have entered the vascular system and begun 

 to move downward in the veins of the leaf (see this monograph, vol. II, p. 308). 



A plunge-experiment similar to the preceding but varied by the fact that the leaves were bruised 

 and wounded more or less before being put into the infected water gave positive results. After 5 days 

 a distinct infection was observed, and a microscopic examination showed the presence of the bacteria 

 even in the stem of the plant, these having passed down through the leaves from the wounded places. 

 In one specimen there was already the beginning of adventive root-formation on the stem. 



Hunger also smeared portions of leaves and stems with pure cultures of Boot, solanacearum, and 

 placed these plants under large bell-glasses with water, so that the atmosphere was always moist. 

 No infections were obtained; the time, however, was rather short (8 days). 



The conclusions drawn are that sound tomatoes are not attacked by Bad. solanacearum, 

 and that infections do not take place through natural openings, such as water-pores. 



According to Hunger, the greatest care should be exercised in planting that the roots be 

 not broken or crushed, and to this end the plants should be removed from the bed and put 

 into the field early, that is, before they have made long roots, which must necessarily be 

 broken in transplanting. He believes that crushing the roots in planting is a common cause 

 of infection. He cites a case in point at Batavia. The disease occurred seriously in the 

 field, and on examination and inquiry he found that the field had been planted not in the 

 ordinary careful manner by an experienced gardener, but that the planting was delayed 

 beyond the proper time and then performed hurriedly. The plants were too large when 

 transplanted ; therefore many roots must have been broken, and they were set out by the 

 gardener with help of two house servants, the coachman, and water-carrier. 



Hunger often found the root-system attacked by a species of Phytophthora, which he 

 says plainly made a passage-way for the bacteria. He is inclined to think that an imper- 

 fectly drained soil is very favorable to the development of this disease. Of this I, too, 

 think there can be no doubt. He made some experiments to determine the effect of animal 

 and plant parasites on the outbreak of the disease. 



In his first experiment, which consisted of pot-cultures in disinfected earth, the surface of the 

 earth was infected with Phytophthora nicotianae from tobacco. The plant was then watered with 

 water which had been infected with a pure culture of Bacl. solanacearum. After 7 days the Phytoph- 

 thora had overrun the entire surface of the earth and had begun to attack the lower end of the stem. 

 After 26 days the plant developed the bacterial disease, and the infection plainly originated from the 

 lower end of the stem. 



In a second set of experiments, made in the same way in disinfected earth, a mole-cricket was 

 buried in the soil of each pot, and the plants were regularly watered with infected water. Ten of the 

 1 1 plants were soon destroyed outright by the insects, the young stem being bitten off underground. 

 One plant remained normal up to the sixteenth day, when it showed the first signs of the bacterial dis- 

 ease; the following day it died. Upon investigation the mole-cricket was found dead in the soil, but 

 the tap-root had been bitten by it, and it is probable that the infection took place through this wound. 



In a third series of experiments, in sterilized earth, the plants were infected with eel-worms 

 (Heterodera radicicola), by mixing with the earth small pieces of roots which had been attacked by 



