482 Brooks. — Observations on the Biology of Botrytis cinerea . 
periments the spores were sown in drops of water upon the leaves. In 
no case, however, was infection brought about. Under the microscope 
it was seen that some of the spores had germinated. The short germ- 
tubes so produced soon collapsed. The explanation of this may be that 
the small amount of poisonous substance secreted at this young stage is 
insufficient to destroy normal tissues. A fuller discussion of this point 
will be gone into later in the paper. The same experiments were tried 
with plants which had been kept some days under a bell-jar and had 
therefore been living in a continually moist atmosphere. It might be 
expected that the tissues of such plants would be more easily penetrated 
by the secretions of the germ-tubes, but no case of infection was observed. 
Kissling recorded the fact that the mycelium of Botrytis caused in- 
fection of a certain host the more speedily, the greater the number of 
‘ generations * the fungus had lived on that host since its origin from a 
sclerotium. This suggested the possibility that spores derived from 
a mycelium which had lived a long time upon Lettuces might perchance 
be capable of infecting normal Lettuce leaves where spores derived from 
the grape extract cultures were impotent. Experiments were repeatedly 
tried with this end in view, but in no case was infection brought about. 
On the other hand, infection was in all cases induced by placing young 
mycelia in drops of the grape extract medium upon the healthy leaves. 
The young fungus invigorated in this way became the victor in its struggle 
with the green plant. 
The effect of wounding normal plants was next tried. Leaves still 
attached to the plants were torn in various ways, and spores placed upon 
the wounded parts. A hot platinum needle was applied to certain of the 
leaves and spores placed upon the burnt areas. In every case infection 
ensued. Of course in such cases the juices which exude from the wounded 
areas provide saprophytic nourishment for the further development of 
the germ-tubes. 
During these attempts to bring about infection by means of the 
spores, it was noticed that certain of the plants, several days after being 
experimented with, showed the well-known disease areas of Botrytis upon 
the lower leaves. It was observed that in all cases the leaves affected 
were becoming yellow. When the diseased area was small it could be 
seen that infection began at that part of the leaf upon which the spores 
had been originally placed. The plants which bore these infected areas 
on the yellowing leaves had been kept under bell-jars in bright light. It 
seemed fair to conclude from this observation that the spores were able 
to infect yellowing leaves although unable to infect those of normal green 
colour. This conclusion was tested repeatedly, and as often confirmed. 
It was apparent from the tests made that Botrytis conidia could bring 
about infection of leaves which had only just begun to turn yellow. To 
