242 



BACTERIA IN RELATION TO PLANT DISEASES. 



(87.) Hubbard squash. This was a very thrifty vine, about 16 inches high, with 6 good leaves. 

 About 50 pricks were made on the middle and apical part of the blade of the fourth leaf which was 

 about 4 inches broad. The eighteenth day there "was no sign of the blight. 



On February 27 the vine was entirely dried up but an examination of the stem showed no bacilli 

 in the vessels or the parenchyma. The Hubbard squashes were planted October 31 and were 

 in small pots. 



(88.) Summer crookneck squash. This vine was about i foot high and had 4 good leaves: 75 

 pricks were made in the blade of the second leaf which was about 2.75 inches broad. 



The wilt did not appear. February 27 the vine was wholly dried up but no bacilli were found in 

 the vessels or in the parenchyma. 



(89.) Summer crookneck squash. This vine was about a foot high and had 4 good leaves: 60 

 pricks were made on the blade of the second leaf which was about 2 inches broad. February 6 the 

 vine was nearly dried up. There was not a trace of bacteria in the stem. Three shoots in a 3-inch 

 pot sufficiently explains the early death of the plant. 



(go.) Potato {Solatium tubernsum). A shoot about 16 inches high was selected for inoculation. 

 Many pricks were made in the middle and upper part of the stem over a distance of about 8 inches. 

 Two leaflets were pricked may times also. No sign of disease appeared on shoot or leaves. 



On February 6 the vine was brought into the 

 laboratory and examined. It was still green and 

 there was no trace of bacteria in the stem. 



(91.) Cucuvabex {Cucuniis sativus). This vine, 

 which was about 16 inches high, was rather badly 

 mildewed at the time of inoculation and some 

 aphides were present. The first and second leaves 

 had shriveled from the mildew. Six good leaves 

 remained. The blade of the fourth leaf which was 

 about 2.5 inches broad was pricked many times. 

 At II a. m. the eighth day after the inoculation 

 there were no signs of the disease, but at 9 a. m. 

 the following day the wilt was of such an extent and 

 character that it must have appeared soon after 

 the previous day's observation. The affected leaf 

 was cut off close to the stem to see if in this way the 

 plant could be prevented from taking the disease. 

 The length of the petiole was 4 cm. The blade was 

 6 cm. long by 7 cm. broad. The wilt was in an 

 irregular wedge-shaped piece (the pricked area) 

 broadening toward the apex (fig. 65). It extended 

 in the vicinity of the midrib, to within i .5 cm. of the 

 tip of the petiole. Fourteen days after inoculation 

 the second leaf above the pricked one was wilted 

 and the following day the first leaf above and the 

 first below the pricked one were wilted and shrivel- 

 ing. The first constitutional signs were 5 days 

 after the removal of the pricked leaf. On the sixteenth day the last leaf collapsed. The day follow- 

 ing the stem was still green and turgid. It was 43 cm. high and had lointernodes. The vine grew 

 from a seed planted September 21. It had been kept in a small pot (4 inch) along with several 

 other vines and was also dwarfed from the presence of mildew {Erysiphe dehor acearum) and aphides. 

 There were blossoms from each node. The diameter of the first internode (hypocotyl) was 3.2 mm. 

 That of the sixth (just below where the inoculated leaf was cut away) was 2 mm. All the leaves 

 were now dry -shriveled. Portions of the stem were saved dry in an envelope for future examination 

 and portions were put into five small vials of alcohol as follows ; (i) Base of pricked leaf and portion 

 of internode above and of one below : The vessels of each bundle were gorged with the bacillus and 

 the tissues were somewhat broken down. There were scarcely any motile bacilli. Only after a 

 long search could I find any whatever and then only a very few. (2) Middle part of the fourth 

 internode: The vessels were gorged with bacilli, although the tissue was apparently sound; there 

 were not many motile rods, although a larger number than in the section in vial i. (3) Third inter- 

 node (not examined). (4) Second internode: The vessels of one bundle were gorged but those of 

 the other bundles were nearly free, some entirely so (?) ; a good many rods were darting and tumbling 

 about, more than in the fourth internode. (5) Middle of first internode (hypocotyl) : None of the 

 vessels were clogged ; some appeared to be free, others to have a few scattering motile rods. 



Fig. 65.* 



*FlG. 65. — Leaf of cucumber plant No. 91 (see text). Drawn by Theodore Holm. 



