774 



bacteria, which, as they issnetl from the cells in vast numhers, {r^xo a milky appear- 

 ance to the water in wliich the section was lyinjf. This beinj; presumably the incij)- 

 ient stage of the disease, it was only necessary in order to trace its development, to 

 select a series of leaves showing more and more ailvan<ed stages of deiay and to 

 examine the pustules successively. This method showed that the bacteria develop 

 rapidly in the tissue of the leaf, raising the epidermis, ami finally breaking through 

 at one or more points in the blaikened area. Oozing through the rujitured tissue, 

 they spread out in a thin, slimy film over the surface in tlie imnu-diate neighborhood 

 of the pustule, linally forming a brown translucent crust of a cheesy c<m.sistency 

 and composed entirely of the bacteria themsfdves. ' * * 



Examination with the microscope showed that there were invariably two forms 

 of bacteria ]iresent, and only two — one in the shape of miinite rods very rarely 

 conneeted in chains, and belonging therefore to tlie genus Macterium, the other 

 consisting of sjdierical cells often united in chains and belonging t<t the genus 

 Micrococcus. » * ' The dimensions of these two forms are, Hacterium 1.9«- 

 3.7//X0.S//. Micrococcus spherical. 0.9//-l.t// in diameter. " ' * It must be 

 noted that two forms of bacteria very similar to those described — a bacterium and a 

 micrococcus — always atcompany and are taken to be the active agents in luitre- 

 factiou whetiu'r of vegetable or animal substances, and the i|uestion naturally arises 

 whether we have here nu-rely a ]>roress of fermentation and ]>utrefa<tiou (what- 

 ev«a' we may lueau by tlieso terms) common ti» all juitreseiMe subst.inces, and 

 induced by the previous growth of some fungus nn the disea.sed spot, or whether wo 

 have to do with specitic agent.s ofdisea.se pc<uli;ir to tobaeco. In this connection 

 it is well to note that a (Jerman investigator, K. Ruchslaud, has recently discovered 

 living organisms btdouging to the Bacteria and t'occi groujis, assotiali'd with the 

 process of fennentatitm of all kinds of tob.icco [see Experiment Station R«'cord, 

 vol. iii,i>. 3'j\ |. A fungus related to one of the ciunmon leaf disi-a.ses of the tomato, 

 of the genus Cladosporium. iloes not occur in sjmts <m tobaeco leaves. Leaves par- 

 tially cured, that is leaves taken at the ]>eriod when the " jiole burn" usually makes 

 its appearaiiee. hut free from any devidojieil fungus and bacterial disease, were 

 ke)d in a damp iituiosiihere for suiue days. I'nder the.se conditions they developed 

 on the leaves in the course of a few days, small brown spots of a velvety a]>i>earance 

 under the m icroscojie, the Cladosporium mentioui'd aboM-. This fungus caused no 

 wiilesjuead damage to the leaf, lu-ing limited to the very small spots in whieh it tirst 

 appeared. In tin* c(Uirse of (> weeks, howivi-r, examination showeil that the fungus 

 was <lecaying r:i]iidly and that in its jdacc vast numbei-s of bacteria were develo)>iug. 

 identical with those found in the poh-burued leavi-s. The gross a]>])earance of the 

 decaying area wa.s similar to that charact<'ristic of '' jiole burn," though, owing to 

 the fact that till' leaves were by this time almost thoroughly curi-d, the spread of the 

 decay was not so ra)>id. Finally, mingled with the bacteria in the ]>ustules of leaves 

 undoubtedly artlieted with ''pole burn," there were often found the remains of a 

 fungus iilentical with the Clados|)orium above mentioned. We may therefore infer, 

 although conelusive results can cuily follow further examination, that " p<de burn" 

 is due primarily to the growth of a fungus u]ioii the leaf, whi<h, by disintegrating 

 and jiartially destroying the tissue of the leaf, gives access to .a bact«'rial process of 

 decay. ' * * 



It is a matter requiring only delicate m.iuipulatiou to isolate the bacteria from the 

 "j>olo-burned " leaves and to obtain i»ure cultures. These were marie in test tubes 

 on both s<did ami li(|iiid media. The bacteria developed readily on jiotatoagar with 

 a slight perci-ntage of tobacco ash ov a trace of jiejitone on slices of sterilized potato, 

 and in potato broth with a trace of ]»e)itone. The sterilized ])otato gave the best 

 results and the cultures have been continued on that substiince. Under these con- 

 ditions the bacteria form on the surface of the pot.tto round or elongated and irregular 

 rtdonies, of a slimy consistency, varying in color from livid gr.iy to dee]> oraii'^e. and 

 producing in the potato ft dark stain beneath mid arninid the colonics. In liiiuid 



