WILT OF CUCURBITS. 251 
green cotyledon separated from the pricked leaf by a distance of 2 cm., was also wilted. At 4 p.m. 
of the same day the vine was brought into the laboratory and photographed along with a healthy 
vine of the same age (Vol. I, fig. 8). The first leaf below the pricked one was examined for bacilli 
in the veins of the blade. They were present but not yet numerous. ‘The leaf-blade had been wilted 
rather more than 25 hours (samples were put into alcohol for the microtome). The blade of the 
first leaf up which was normal at 3 p. m. the previous day but, had wilted 
either the morning of the seventh day or the previous night, was also 
examined: The spiral vessels at the apex of the petiole contained numerous 
bacilli. The veins of the blade were not examined but samples were put 
into alcohol for sections. Bacteria were also found in the vessels of the 
uppermost small leaf at the junction of blade and petiole. The petioles of 
these leaves (pricked one included) were rigid and neither these nor the 
stem had changed color. For the appearance of a single infected bundle 
in cross-section see fig. 69. For appearance of a whole petiole in cross- 
section with low magnification consult Vol. I, pl. 3. 
(151.) Cucumber var. White wonder (Cucumis sativus). Many pricks 
were made in a basal lobe of a leaf about 2.25 inches across. The morning 
of the fifth day the first slight trace of the wilt appeared in the pricked part 
of the leaf. At 2p. m. the wilted part was duller green and covered an area 
of nearly 1 sq. cm. in the middle of the pricked part. The following day 
(3 p. m.) there was only a small increase of the wilt: Not one-twentieth 
of the leaf-blade was involved. The eighth day about one-fourth of the 
pricked leaf was flabby and the middle of the diseased area was now brown 
and dry. The following day the pricked side of the leaf was dry-shriveled 
and the rest of the blade had wilted. ‘The petiole and the other leaves were 
turgid. The ninth day the first leaf down (3 cm. below) wilted and the 
following day the first leaf up (2 cm.) drooped its blade. The second leaf 
up was then turgid (9 a. m.), but at 1 p. m. its blade was drooping. The 
petioles were still rigid except that of the first leaf down which was a very 
slender one. The fifteenth day after inoculation all the leaf-blades were 
wilted but the stem and all the petioles were green and turgid. Thin sec- 
tions of the blade of the second leaf up were now examined under the micro- 
scope and the bacilli were found to be plentiful in the spirals of the leaf- 
blade and forming cavities around them. ‘They were apparently not in the 
’ green parenchyma-cells. Portions of the petiole of the pricked leaf were 
put for 2 minutes into boiling absolute alcohol containing 1 per cent picric 
acid and were then transferred to 75 per cent alcohol which was repeatedly 
renewed, i. e., until all the picric acid was removed. Other portions were 
fixed directly in 75 per cent alcohol. The first mentioned fixative gave the 
best results. The petiole of the pricked leaf was also examined microscopi- 
cally. The vessels were gorged with bacilli and the primary vessel-paren- 
chyma was broken down. 3 
(152.) Winter Squash var. Sibley’s or Pikes Peak (Cucurbita sp.). 
Many pricks were made on a leaf 3 inches broad, on one side about midway 
from the base to the apex of the blade. The ninth day there was no trace 
of the wilt, nor did it appear later. 
(153-) Winter Squash var. Sibley’s or Pikes Peak. Many pricks were 
made on the apical part of a blade about 2 inches broad. 
‘There was no result from the inoculation. 
(154.) Winter Squash (same variety). Many pricks were made on one 
side of the blade of a leaf about 2.5 inches broad. 
No result. 
(155.) Winter Squash (same variety). This was growing in the same pot as 154. Many prieks 
were made on the apex of the blade of a leaf about 2.25 inches broad. 
There was no result from the inoculation. 
*Fic. 68.—B, cross-section of a squash-leaf wilted by Bacillus tracheiphilus, showing that wilt of parenchyma is due 
to cutting off water-supply rather than to actual occupation of parenchymatic tissues by the bacteria. At base is 
a bundle destroyed by the bacteria. Beyond this is a long wilted area in which no bacteria occur. Only a portion of 
this wilted area could be shown in the picture, the whole length being shown in fig. C; the portion represented in the 
drawing corresponds to the black part of C. A, neighboring uncollapsed portion of the same leaf, the bacteria in this 
being confined to a portion only of the vessels of the bundle. Slide 362-1, lower row, last section but one at the right. 
Drawn with a Zeiss 8 mm. apochromatic objective, No. 12 eye-piece, and Abbe camera. 
