of Bacteria and their Allies by Heterogenesis. 391 
of the bottle wet with the formalin solution. The bottle was 
subsequently left in a cupboard for seventeen weeks, the 
temperature of which for a long time remained about 70° F., 
although it afterwards fell to 55° F. 
When removed from the bottle at the expiration of this 
time the potato was found to be quite firm and noé at all 
shrunk. On section it was seen to be discoloured to a pale 
earthy tint, with mottlings here and there of a rather darker 
colour. The cut surface was moist and had a distinctly acid 
reaction, and there was not the least sign of softening or dis- 
integration anywhere. Thin sections having been made, they 
were shaken up in a small tube with distilled water, so as to 
get rid of the starch-grains from many of the cells, and the 
sections were subsequently allowed to soak in some of 
Westphal’s mastzellen stain, diluted with 2 per cent. formalin, 
for two hours. 
On microscopical examination of these sections groups of 
Bacteria were found in large numbers of the cells, and every- 
where except in those near the surface. ‘The contents of one 
of these cells is shown in Pl]. X XV. fig. 2, B (x 500) ; some of 
the Bacteria were free and others were in or lying on the 
primordial utricle, but, as I have usually found with micro- 
organisms in such situations, they were not appreciably 
stained. Some cells, which did not contain obvious Bacteria, 
showed plenty of minute cocci-like bodies on the surtace of 
the primordial utricle, also not taking the stain, which pro- 
bably represent early stages of the Bacteria (fig. 2, A, x 700). 
Another larger potato, about two inches in diameter, was 
treated in exactly the same way as the last, in September 1901, 
and after the bottle was finally closed it was left on the 
surface of an incubator at a temperature of about 80° F. for 
seven weeks. 
When examined the potato was not found to have shrunk 
or to be appreciably altered on the surface. On section it 
was moist, of acid reaction, and showed as before a pale 
earthy colour with rather darker mottlings. 
Sections were made and treated in the manner previously 
indicated, and on examination multitudes of Bacilli were seen 
here and there in cells in all parts of the section except for 
about one fifth of an inch from the surface. In places also 
there were fine mycelial filaments containing spore-like 
bodies. Some of these Bacilli took the stain fairly, as may 
be seen in Pl. XXV. fig. 3, A (x 500), in which the two kinds 
of organisms are shown. In or on the primordial utricle also 
there were multitudes of very delicate interlacing filaments 
(? Bacilli), containing an abundance of spores which had 
26% 
