WILT OF CUCURBITS. 



231 



first leaf below was now flabby on one side and the second below was drooping slightly and lacked 

 its normal turgor on one side. In both cases the affected side of the leaf was anatomically nearest to 

 that part of the stem which was in direct line with the insertion of the pricked leaf. By 4 p.m., the 

 third, fourth and fifth leaves above were flabby. The first and second below were entirely limp and 

 drooping. The third below was losing turgor at the apex. The morning of the twelfth day all the 

 small leaves at the apex, above the fourth leaf up, were flabby but there were no further changes. 

 At 5 p.m., the third leaf below was still turgid. The inorning of the fourteenth day there was still 

 a small portion of the base of the petiole of the pricked leaf which was turgid. The flabby portion 

 just above this was yellowish. The blade of the third leaf below was now flabby. This was separated 

 from the next leaf above by a long internode. Nothing now remained free from signs of the wilt 

 except the stem. The upper portion of the vine was removed and taken into the laboratory for 

 microscopic examination. The vessels were found to be full of the bacillus which strung out in fine 

 gummy threads from the cut surface of the stems. A part of the vine was put into alcohol for paraffine 



Fig. 63.* 



sections and the rest was saved dry to search for spores. The bacteria were exceedingly abundant 

 in the stem and the inner tissues were considerably broken down. The organism was cultivated out 

 and found to be Bacillus tracheiphilus. My method in this case was as follows: The stem was cut 

 with a sizzling hot knife, a hole was then worked into the end 3 to 5 mm. deep, i.e., below the burned 

 surface, using a stiff, sterile steel needle. The stem was then squeezed a little, and fluid was trans- 

 ferred from the bottom of the moist cavity into sterile potato broth, using a freshly flamed small 

 platinum oese. In this way four broth-cultures were made from the interior of this plant. Subse- 



*FlG. 63. — Inoculated leaf of cucumber plant No. 28, shaded to show gradual progress of wilt. Dots indicate 

 needle-pricks. The first wilt appeared some time between fifth and sixth day after inoculation. At end of 5I davs 

 (morning) 2 was wilted and I shriveling; on afternoon of same day J was wilted; the next morning 4 had wilted. 

 I3y the eighth day thewhole blade had wilted and two-thirds of it had shriveled. Plant inoculated Oct. 25, 1894. 

 Drawn by Theodore Holm. 



