SPECIAL A( rol'NT. 



17 



outer ])ortioii of tho root whicli luis come into direct loiituct with the 

 fimjii and Imi-teriu of the soil, and whicli would Ih' more or less rotted 

 if tli«' or«;anisni had entered the plant from the earth. If the infeetion 

 had l>«'en from tlu' soil, the root would al.M) have contained a mixture of 

 thing's anil not one species in pure culture, and certainly not I'x, ciini- 

 jit'stris, since the soil was not ol>tained from calihuiie fields, and all the 

 numerous uninoculated turnip plants o;rown in it ivmained entirely 

 free from this disease. 



The foUowine- photomicrocrniphs ar(> all made frotu sections of this 

 root at level No. •-^ (See frontispiece and 1*1. III.) 



PI. V. ti"-. 1, lepresents a lonji-itudinal section through ;i small Itun- 

 dle fully occui)ied 1)V the bacteria and deeply stained. The maenitica- 

 tion is not sufficient to show the individual oruanisms. hut it can no 

 made out (juite clearly that tlie surroundinu" parenchyma i> not occu- 

 pied and that there is as yet no disorifunization of the tissues. The 

 second lijrure on this phite is :i lonjjitudinal section throuifh two small 

 vascular bundles. The knife i)assed throu*i-h the middle of the lower 

 ])imdle and the extreme margin of the ujjper one. The tissue around 

 -the u})per bundle is just becomini'' h()lU)wed out into a cavity, that 

 around the lower one is still intact and unoccupied by the ])acteria. 

 The vessels themst^lves are crowded full of the ore;anism. 



Three of the reproductions on PI. VI are from cross sections of 

 small bundles, i. e.. bundles similar to those illustrated in PI. \'. In 

 the lower riuht-hand corner is a cross section showing a single vessel 

 occupied by the l)acteria, the rest of the tissue being entirely free. 

 In the lower left-hand corner are several vessels so occupiml: tho 

 larger one, however, contains only a narrow film of ])acteria (around 

 the walls), which may have entered from a))ove or l»elow. or at this 

 level, through the side of the vessel next to the more fully occupied 

 part of the bundle. The surrounding tissue here is also entirely free 

 from these organisms. The iipper figure on this plate corresponds 

 more nearly to the lower figure on PI. V. Here several ve.ssels are 

 occupied, together with their connective tissue and the surrounding 

 parenchyma, and we have the first stage in the formation of a l)acterial 

 cavity. The left-hand side of this figure is shown more highly magni- 

 fied on PI. IX, fig. I. The middle figures at the left show the manner 

 in which the bacteria crowd apart parenchymatous cells, multiplying 

 first in the intercellular spaces and either dissolving or splitting apart 

 the middle lamella, probably both. The middle figure at the right is a 

 cover glass (smear) of Ps. eampestrls stained Avith carliol f uchsin and 

 mao-nified 1,000. It was made directlv from the vessels of a cabbage 

 plant and is the only figure not taken from the turnip. 



On PI. VII are two additional figures showing early stages in the 

 occupation of small bundles. Nonlignified wood-parenchyma cells 

 are also occupied, at least in fig. 2. The surrounding tissues are 

 9228— No. 29-02 2 



