278 
The blight bacterta.—Considerable has been said im 
previous reports about the organisms which cause blight, 
and it will be well to give illustrations! of them in this con- 
nection, to fix the fact that we are not dealing with 
bacteria in general, but with a single species. 
HRC Figure 1 shows the individual bacteria, greatly 
5° og. Magnified, as they exist in the tree during disease. 
° “0 ° Some of the younger cells are usually to be seen 
9 still united in pairs, indicating the mode of multi- 
Fig. 1-Bac- plication by bipartition. Figures 2 and 3 show 
teriain pear forms of zodgloea vary- On id 
blight from jing according to age. LENS 
a culture in The older ones are ~ agi 
hay infus- ‘ ua ari 
ion. Magni- More irregular and Cory Slee 
fied 890 di- with a convoluted sur. Piss ee A foo an 
ameters. face. These masses, dics () 
@ ~ 
like the zodgloea of other species 7-475 
of bacteria, consist of a colorless Wael sak Mea Wie it 
substance of a gelatinous consis- + aie 
tency in which the bacteria are Fig. 2.-Small zooglea from a 
thickly imbedded. This ground Poth a te ae el 
4 : if 2 n 
substance sometimes extends hitthe Magnifie asooaiiiee sacah 
beyond the mass of bacteria, as 
in figure 4, forming a clear envelope, which separates the 
mass from the surrounding bacteria. It is generally con- 
ceded that this is a resting state of the organism. 
In the case of pear blight 
the zodgloea have only been 
observed in liquid cultures, 
and not in the tree. At what(*, Ss 
time or under what circum-¢/¢ ~¢ \ 
stances they occur in nature, “<: * 
it is impossible at present to J.-S \ 
say, but it is not likely to be Yo 
while the bacteria remain in  \,. 
the tree. 
The form of these zodgloea 
is one of the most characteris- 
tic features in the develop- 
‘ment of the blight bacteria. 
A more extended and syste- 
matic description of the species 
and its development has been Fig. 3.—Zooglea from a culture in 
published elsewhere, ? to which potato infusion. Magnified 890 
the reader isreferred for furth- diameters. 
er information. 

‘Taken by permission from the Proceedings of the Phila. Acad. of Nat. 
Sciences, 1886, Pl. ILI, from an article by the writer. 
*Burrill in Amer. Nat., Vol. VII, 1883, p. 319 ; Arthur in Proc. Phila. 
Acad. Sci., 1886, p. 317. 
