WILT OF CUCURBITS. 



225 



bell-jar. The first three vines were used as checks on the behavior of the fourth. The air 

 under the bell-jars was quite moist and at 4 p.m. water stood in tiny beads on the margin of 

 the leaves. At the end of 24 hours the under surface of the sprayed leaves was still wet in 

 places especially that of the leaf on which the aphides were colonized. Some of the latter 

 had migrated to other leaves. All were sucking the plant juices and for fear of mechanical 

 injury I brushed off and destroyed most of them. None were observed on the check vines. 

 The bell- jars were removed and the plants exposed to the air for half an hour to dry off a 

 little and then the jars were put back. This 

 was done frequently during the experiment. 

 The fourth day the vines were still healthy 

 and the checks were free from aphides. 



Tube 8, October 23, was inoculated from 

 a very sticky potato culture (tube 8, October 

 17), which was inoculated from a single, small, 

 white colony on a slant agar culture streaked 

 September 2 7 from tube i , September 1 7 , which 

 was inoculated from the interior of plant No. 2. 



(20.) Cucumber (check). Plant about 5 

 inches high with two well-developed leaves and 

 one more coming, also two green cotyledons. 

 The bacterial fluid was sprayed on the under sur- 

 face of the two largest leaves and the plant was 

 then put back under the bell-jar. The eight day 

 after spraying, this vine was still healthy. It had 

 grown an inch or two since October 25. It was 

 still free from ants and aphides. Two days later 

 it was healthy and growing rapidly. The twenty- 

 third day the bell-jar was removed and not re- 

 placed as the plant was beginning to be spindling 

 although no trace of the disease had appeared. 

 The thirty-fourth day the vine was still free from 

 the disease but had remained spindling since the 

 removal of the bell- jar. By the fifty-first day 

 the plant had lost all its leaves and the tip of the 

 stem had wilted. It was not much over i foot 

 high, having never recovered from the stunting 

 due to keeping it under the bell-jar. Thin sections 

 were cut and a microscopic examination made, 

 but no bacteria were found in the vessels. 



(21.) Cucumber (check). This plant was the 

 same size as No. 20. It had two green cotyledons, 

 bore one well-developed leaf, which was sprayed 

 on its under surface, one twisted deformed leaf, 

 and two undeveloped leaves. After spraying 

 it was placed at once under the bell-jar. The 

 eighth day this vine resembled the preceding in all 

 particulars. It remained healthy and grew rapidly for a time but on the final removal of the bell-jar 

 (the twenty-third day) it was beginning to be spindling although free from the disease. The thirty- 

 fourth day it was still free from wilt but had remained spindling. The forty-sixth day it was brought 

 into the laboratory and examined for the presence of the bacillus in its tissues. It had never recovered 

 from the stunting due to keeping it under the bell-jar. Since the removal of the latter it had also 

 suffered to some extent from mildew, from aphides, and on two or three occasions from insufficient 

 moisture. It was not over 12 inches high. For the 3 weeks preceding it had been losing its foliage 



*FiG. 59. Cucumber No. 18, inoculated at x by needle-pricks with a pure culture of Bacillus tracheiphilus on Oct. 

 i, 1894. Numbered parts were removed and fixed in alcohol Oct. 16. They were subsequently embedded in paraffin, 

 sectioned and stained for presence of bacteria, which were found in vessels at all points marked +, and not at those 

 marked . They occurred in greater or less numbers according to distance from inoculated leaf, or from main axis. 

 Exclusive of wilt there were no surface indications of disease. About one-fourth natural size. 



Fig. 59.* 



