338 Edwin F. Hopkins 



always been observed when the acidity was approximately +20 according 

 to Fuller's scale. Perhaps the range is as wide as that determined by 

 Munn (1917:407-108) for the growth of Botnjtis Allii. 



Conidia production 



Although conidia are produced abundantly in nature on tulip leaves, 

 in agar culture under the ordinary laboratory conditions they rarely 

 appear. The fungus tends rather to form sclerotia. However, early in 

 1917 the writer observed for the first time that conidia had formed under 

 these conditions when some conidiophores developed in five petri-dish 

 cultures. It should be noted that these conidia were produced without 

 any special treatment, and that, although they were produced once or 

 twice afterward, this is rather unusual under the conditions obtaining 

 in ordinary culture vessels. 



On March 17, 1917, sterilized tulip leaves in large test tubes, 20 x 2.5 

 centimeters in size were inoculated with cultures of three different strains 

 in duplicate. In two of these strains a fluffy mycelium soon developed, 

 which spread along the leaves. After about ten days conidiophores began 

 to develop, usually toward the top of the culture, and by March 31 there 

 was an abundant development of conidiophores close to the surface of 

 the leaves just beyond the aerial mycelium as well as on the mycelium 

 itself. The conidia produced were able to cause infection in healthy 

 tulips. This experiment was repeated on April 27, 1917, and the cultures 

 were observed daily in order to note the first appearance of the conidia. 

 This occurred in five cultures on May 8. 



Some time later, Professor Whetzel suggested that a partial drying of 

 the plate cultures, after a good growth of mycelium had started, might 

 produce conidia. This experiment was accordingly performed, and the 

 partial drying was accomplished by so placing the petri-dish cover as to 

 expose part of the agar surface, thus permitting more rapid evaporation. 

 The petri dishes were usually left overnight in a dust-free chamber and 

 were tightly covered again the next morning. Conidia were in this way pro- 

 duced successfully in a large number of instances, not only from B. Tulipae, 

 but also from other Botrytis species which do not readily fruit in culture. 

 On halves of sterilized tulip bulbs in petri dishes the fungus was also 

 found to fruit abundantly. There seems to be a relation between conidia! 



