298 Mr Brooks, Notes on the parasitism of Botrytis. 
Notes on the parasitism of Botrytis. By F. T. Brooks, B.A., 
Gonville and Caius College. (Communicated by Mr F. F. 
Blackman.) 
[Read 20 May 1907.] 
The conidia of Botrytis are unable to infect healthy green 
leaves, whereas if a young mycelium, nourished saprophytically, is 
placed upon a normal leaf of such a plant as Lettuce, infection 
rapidly spreads. 
Experiments have been undertaken to ascertain whether the 
conidia can cause the infection of plants weakened in various 
ways. Lettuce plants were grown in sterilised sand which was 
watered from time to time with different mineral solutions. One 
group of plants was watered with a solution containing the 
elements essential to ordinary plant life, while the other groups 
were watered with solutions containing no nitrogen, phosphorus, 
potassium and magnesium, respectively. After these plants 
had been growing six weeks the conidia had no power of infecting 
them. 
On the other hand it was found that by tearing healthy green 
leaves of Lettuce plants direct infection was caused by placing 
the spores upon the torn portion. The conidia are able also to 
infect leaves just beginning to turn yellow — whether this 
yellowing occurs in ordinary light or after placing the plants 
in darkness. 
