TECHNIQUE EMPLOYED. 15 



and of outtinji:. aiul tho subsoquoiit t'astoiiino- to tho slido and caivful 

 inaiiii)ulatioii duriiiu- t\\v removal of the i)aratlin. the iiydratiiig-, stain- 

 ing, ditfeivntial l)loachinii\ dehydrating, and mounlini;- proeesses leaves 

 no douht whatever that the location of the bacteria in the tissues, as 

 shown in the photoniicrographs, is the same as in the fresh root. There 

 has been no tearing of these bacterial masses or shoving oi- crowding 

 of them into parts of the root where they were not originally present, 

 such as Avould naturally occur in making sections of living or unintil- 

 trated material. In some cases tlie more delicate parts of the root 

 have V)een broken a little in places, as already mentioned, but only to 

 a slight extent, which in no way interferes with one's judgment as 

 to the effect of the bacteria upon the root. Indeed the process of 

 fixing renders the l)acterial layer tougher and less liable to shoving 

 or rupture l)y the knife than any other part of the root, as may be 

 readily seen from an inspection of my sections. The bacteria in the 

 sections have ttiken a deep purple stain, and, there being very little 

 ground stain, the individual rods stand out clearly under the oil- 

 inuuersion lens, nuich more clearly than in the photomii-rographs. The 

 sections are remarkaldy good, but owing to their thickness (»'. /< to 10 /i) 

 a number of lavers of bacteria lie one behind the other and seriously 

 interfere with the photographic image. Ver}' likely also a more expert 

 photomicrographer would be able to make more out of the sections 

 than the writer. Attempts were made to cut thinner sections, but the 

 material did not seem well adapted to very thin sections. In those 

 2-4 // thick there was so much shoving together and tearing that the}' 

 could not be used. 



SPECIAL. ACCOUNT OF THE DISEASED PLANT. 



On PI. II ma}' be seen a cross section of the lower part of the root, 

 magnified 50 times. The section was taken from the point marked "3" 

 on the frontispiece. The bleaching process subsequent to the staining 

 has been carried so far that the root is only slightly stained, except 

 where there is bacterial occupation of the vessels and wood parenchyma. 

 The actual size of this section is indicated by a circle at the bottom of 

 the plate. 



The extent of bacterial occupation and disorganization in the inte- 

 rior of the root is very interesting. In one of the cross sections of 

 this root, made higher up than that shown on PI. II and involving- 

 less than one-half the circumference, the writer counted 93 distinct 

 centers of bacterial infection and 15 bacterial cavities, involving in 

 cross section from 50 to 300 cells each. In a cross section from nearly 

 the same level as PI. II, 146 distinct groups of bacteria were counted 

 in the vessels. In the photograph here reproduced it will be observed 

 that the bacteria are confined to the inner portions of the root, princi- 

 pally to the vessels and the surrounding nonlignified wood parenchyma. 



