no Brown . — Studies in the Physiology of Parasitism. VI I L 
The effect of the addition of extraneous nutrient to the infection drop 
is to accelerate the incidence of attack (e. g. attack of Betrytis on petals 
of Rose, &c.), or in extreme cases to bring about attack where no attack takes 
place in its absence (e. g. attack of Botrytis on leaves of Broad Bean). In the 
case of a plant which allows a considerable amount of nutrient to diffuse into 
the infection drop, one would anticipate that the time required for spores 
sown in water to produce infection would approximate to that required for 
spores sown in nutrient extract, whereas the difference in time would be 
more marked in the case where less nutrient was allowed to pass out. 
An experimental difficulty is met with in the fact that Botrytis spores 
of a certain type are able to germinate to some extent in pure water, and 
it is highly probable that this degree of germination is sufficient to enable 
them to attack delicate structures such as petals even without the addition 
of any nutrient to the infection drop. In order to make the results more 
sharply marked, measures were therefore taken to suppress the germination 
of the spores in pure water. 
The first method depends on the fact that the germinative capacity of 
Botrytis spores is reduced by age. Thus, while a suspension of young 
spores (io days from sowing of cultures) will readily germinate in pure 
water, those from a six-weeks old culture will no longer do so, though they 
are quite capable of germination in nutrient. Using spores of these two 
types the following results were obtained in comparative infection experi- 
ments with Cereus (considerable exosmosis) and Gloxinia (small exos- 
mosis) : , 
Type of spore. 
Sown in. 
Plant. 
Time for infection 
in all the drops. 
Young 
Turnip extract 
Cereus 
io-i r hours 
* >> 
Water 
II-I2 „ 
Old 
Turnip extract 
>> 
20-23 „ 
Water 
22-26 ,, 
Y oung 
Turnip extract 
Gloxinia 
13- i 6 ,, 
Water 
j? 
23-26 „ 
Old 
Turnip extract 
55 
3°-34 » 
>> 
Water 
none in 96 hours 
The points brought out in the above table are as follows : 
i. The time required for infection by the old spores is always greater 
than that in the case of the corresponding infection by young spores : in 
the present experiment about twice as long in each case. 
1. In the case of Cereus, both types of spore attack the petal almost 
as readily when sown in water as when sown in turnip extract. In the case 
of Gloxinia, the spores sown in water attack distinctly more slowly than 
the corresponding sowings in turnip extract. This is especially the case 
when the old spores are sown in water. Here no attack takes place even 
after four days, thus showing that the spores have been unable to obtain an' 
appreciable amount of nutrient from the plant. When, on the other hand, 
