WILT OF CUCURBITS. 



2 47 



see if the disease could be prevented from entering the stem.* Two days later the first leaf down had 

 shriveled. The eleventh day the vine was brought in and examined in three places, i.e., (i) at the base 

 of the pricked leaf which was removed, (2) at the lower end of the same internode, (3) at the upper 

 end of the next lowerinternode, i.e., just below the last leaf to wilt. Not a trace of bacilli were found 

 in the vessels or parenchyma, i. e., the disease was cut out. This leaf (the last one on the vine) probably 

 shriveled from the attacks of mildew, aphides and old age. 



Remarks. This virulent culture promptly attacked the eight muskmelons and the 

 one cucumber, but had little or no effect on the squashes. It caused no disease in potatoes, 

 tomatoes, hyacinths or pear. Theoretically it should have attacked the squashes readily 

 and their behavior was a great puzzle. In five of the melons signs appeared on the same 

 morning, i. e., 4*4 days from the insertion of the bacteria. 



Inoculations of January 12, 1895. 



Two squash-vines and one muskmelon-vine were inoculated with fluid taken directly 

 from the interior of the inoculated wilted muskmelon vine No. ma 

 in which a microscopical examination had shown bacteria to be 

 present. Many pricks were made with a small steel needle. 



(1 14.) Summer Squash (Cucurbita sp.). Many tiny pricks were made 

 on the blade of an upper leaf. On January 25, the pricked leaf-blade and 

 two-thirds of the petiole were wilted (they were turgid the morning of 

 January 24). This leaf was now removed and the petiole examined care- 

 fully, but I did not find any evidence of bacteria in the vessels or the 

 parenchyma. The leaf was badly attacked by mildew. 



February 25 there was no wilt, and on microscopic examination I 

 could find no bacteria in the tissues of the stem. 



(115.) Hubbard Squash {Cucurbita sp.). Many tiny pricks were 

 made on the blade of one of the upper leaves. 



February 27 there had been no wilt and three sets of sections from 

 the stem at different heights showed no bacteria in the tissues. 



(116.) Muskmelon (Cucumis melo). This vine which was a small one 

 was pricked rather carelessly many times on the blade of a small leaf and 

 held as a check on the aquashes. The first wilt appeared the ninth day 

 on the blade of the pricked leaf, involving about half of it. The following 

 day the blade and petiole of the pricked leaf had begun to shrivel. The 

 vine was brought in and its interior examined microscopically. The base 

 of the petiole was full of the bacilli, a large proportion of which were very 

 actively motile. The motions consisted of a straight ahead, sinuous, slow 

 or rapid movement for long distances in all directions ; a somewhat slow, 

 curved movement carrying the rods long distances; and a slow or rapid tumbling motion. 



Remarks. Up to February 28, 1895, the experiments with squashes were very dis- 

 couraging. The failure to induce the wilt with virulent bacteria, capable of wilting cucum- 

 bers and muskmelons in from 6 to 10 days when introduced simply by needle-pricks (as 

 shown repeatedly by control inoculations) remained unexplained. Squash after squash 

 was examined microscopically with great labor, but with exception of No. 79 and 104 a, no 

 bacilli were found in the tissues. The inoculated plants were inspected day after day for 

 many weeks, but none of them exhibited any distinct signs of secondary wilt, with the 

 possible exception of No. 79. In case of a few plants inoculated late in the autumn a small 

 wilted area appeared in the vicinity of the pricks, but did not increase much after its first 

 appearance. In most of the squashes (36 were inoculated) no primary wilt appeared. 



My conclusions at this time were that the squash-disease must be due to the organism 

 causing the melon- wilt and cucumber-wilt. 



"The whole of the petiole (exclusive of a few sections from the base cut to examine microscopically) and the lower 

 part of the midrib were put into alcohol along with the upper and partially wilted portion of the blade, for paraffin 

 infiltration. It is important to determine how generally diffused in the parenchyma the bacteria are when the wilt 

 and change of color (to pale green) occurs. Query : Does this depend on destruction of tissues or only on lack of water? 

 (See fig. 68.) 



fFiG. 66. Leaf of inoculated plant No. 1 13 (cucumber) showing pricked area and extent of wilt on eighth day. 

 There was none on seventh day. From basal part of wilted area to stem was a distance of 7 cm. (see text). 



Fig. 66.f 



