BACTERIAL WILT OF CUCURBITS. 11 



larger and larger number of beetles have the opportunity to feed on 

 diseased plants and so to become possible wilt carriers. Thus the 

 maximum number of actual wilt carriers comes not simultaneously 

 with the maximum beetle prevalence, but after that maximum; that 

 is, at some time during the downward progress of the beetle-prevalence 

 curve. 



STOMATAL INFECTION. 



Since the last publication on the subject by the writers 1 further 

 attempts at stomatal infection have given uniformly negative results. 

 Unless the epidermis is wounded and the wilt organism introduced, 

 infection apparently never takes place. 



SOU, INOCULATIONS. 



As reported in a previous article, 2 the only cases in which we have 

 been able to transmit wilt through the soil have been those where heavy 

 tap-water suspensions of virulent bacteria had been poured directly 

 around the roots of potted plants. In these cases sufficient water 

 was used so that it would im m ediately percolate through the soil 

 to the roots, and some of the plants were root pruned on one side. 

 Only a small percentage, even of the root-pruned plants, became 

 infected, and exa m i n ation of the roots of nonroot-pruned plants 

 which had wilted usually showed injuries from transplanting, from 

 nematodes, or from other causes. 



During 1916 and 1917 several further series of soil inoculations 

 on potted cucumber plants were carried out in a similar manner. 

 The virulence of the heavy tap-water suspensions of the bacteria 

 was established in each case by needle-puncture inoculations made 

 just before pouring into the soil. Briefly, the results are as follows : 



March 31, 1916. All had been recently transplanted. (1) Xot root pruned, 36 

 pots, 2 plants to a pot; 22 per cent -wilted. (2) Root pruned, 24 pots, 2 plants to a 

 pot; 25 per cent wilted. 



April 19, 1916. All had been transplanted. (1) Not root pruned, 30 pots, 2 plants 

 to a pot, 23 per cent -wilted. (2) Root pruned, 18 pots, 2 plants to a pot; 39 per cent 

 wilted. 



April 19, 1916. All these plants were grown in the pots without transplanting. 

 (1) Xot root pruned, 36 pots, 2 plants to a pot, 2.8 per cent wilted. (2) Root pruned, 

 24 pots, 2 plants to a pot, 29 per cent wilted. 



December 7, 1916. All these were old plants and not recently transplanted. 

 (1) Xot root pruned, 4 pots, 1 plant to a pot, no wilt. (2) Root pruned, 4 pots, 1 

 plant to a pot, 50 per cent wilted. 



December 7, 1916. All these were young plants recently transplanted. (1) Xot 

 root pruned, 27 plants, 3.7 per cent wilted. (This plant showed the roots badly 

 gnawed. Examination of the roots of 8 of the non wilted plants failed to show any 

 root injury.) (2) Root pruned, 9 plants, 55 per cent wilted. (Examination of the 

 roots of the 4 nonwilted plants failed to show root injury. In running a knife into 

 the soil the main roots at least must have been missed.) 



> Rand, F. V., and Enlows, Ella M. A., 1916. Op. cit., p. 425. 

 2 Rand, F. V., and Enlows, Ella M. A., 1916. Op. cit., p. 423. 



