286 Brown. — Shidies in the Physiology of Parasitism. IX. 
considerable, and a hitherto scarcely suspected, part in influencing the 
germination of the spores of fungal parasites. 
The most significant statement in the literature dealing with this subject 
is that of Neger (2), who observed that spores of Bulgaria polymorpha 
germinate better in hanging-drop cultures when pieces of oak, beech, &c., 
bark or wood, were placed in the bottom of the cell than when they were 
absent. Neger makes no statement as to the nature of the substances pro- 
ducing this effect. 
As we are undoubtedly concerned here with volatile organic substances 
which produce stimulation of germination when present in very low con- 
centration, reference may be made to the work of Duggar ( 3 ), who states 
that traces of ethyl alcohol or ether cause increased germination of the 
spores of Aspergillus. Duggar further records that distilled water which 
has been kept for some time in paraffin-lined flasks produces better germina- 
tion of the spores of Aspergillus flavus than similar distilled water which has 
not been in contact with paraffin. Similarly the presence of vaseline in the 
hanging-drop cultures was found to improve the germination of Aspergillus 
flavus spores by io to 20 per cent. 
As a striking illustration of the influence of small traces of a volatile 
organic substance, we may cite the work of Beijerinck and van Delden (4), 
who describe a bacterium, called by them Bacillus oligocarbophilus , which 
did not grow in a nutrient containing a source of carbon food, but made 
appreciable growth in the absence of the latter from the cultural solution. 
These workers showed that the source of carbon in the case of this bacterium 
was some volatile carbonaceous substance present in the atmosphere, but 
which was not carbon dioxide. As to the nature of this substance, they 
were not able to make any statement beyond the fact that it was more 
abundant in laboratory than in greenhouse air. 
The usual method of experiment in the present work was to lay the 
plant organs in question in large Petri dishes side by side with clean slides 
on which drops of an aqueous suspension of spores were placed. In 
a limited number of experiments, as will be mentioned later on, the plant 
structures were placed in the bottom of large containers and the slides 
placed in a rack above. As in general the effects were more marked when 
the leaves, &c., were first bruised, the rule was made to put the leaves into 
the Petri dishes first, and then after a time the slides, so as to avoid any 
risk of droplets of plant juice falling on the slides. Also the bruising 
operation was always done at some distance from the Petri dishes, in most 
cases in another room. Petals of Rosa centifolia were always washed first 
of all to remove any adherent pollen. 
As regards the cleaning of glassware, preparation of spore suspensions, 
&c., the usual methods were adopted. Ordinary distilled water was used 
throughout. In the earlier stages of the work the Petri dishes were washed 
