The Botrytis Blight of Tulips 339 



production and the relative humidity over the culture, or, to state it more 

 concisely, a relation between the rate of evaporation and conidial pro- 

 duction. 



There is, perhaps, something inherent in the nature of the host tissue 

 which makes it an especially good substratum for the production of 

 conidia; but it is more likely that the fungus finds in such cultures more 

 variation in the moisture relations. This would explain why, in the 

 experiments with sterilized tulip leaves, the conidia were not produced 

 uniformly throughout the culture but only on a limited area toward the 

 top of the culture tube, where the moisture relations were presumably 

 most favorable. 



Dissemination of conidia 



The peculiar twisting of the conidiophores, already mentioned, is 

 thought to have some relation to the dissemination of the conidia. In 

 the first place, the conidia fall away very readily. This becomes obvious 

 when an attempt is made to mount conidiophores bearing conidia in a 

 liquid medium or if a conidiophore is jarred slightly. Secondly, the 

 conidiophores are very hygroscopic, and a small change in the atmospheric 

 moisture will cause them to twist with considerable violence and frequently 

 even to dislodge the conidia. This phenomenon can be easily observed 

 in this and in other Botrytis species by placing the specimen under a 

 binocular microscope. Merely breathing on it gently suffices to produce 

 these contortions. It may be concluded that in nature, owing to the 

 frequent changes in humidity that occur, conidia are commonly dislodged 

 in this manner and carried off by air currents. 



The conidia are usually wind-borne. The writer has found that 

 inoculations with conidia are best made by either blowing or dusting 

 them on the host plants and subsequently spraying water on them with 

 an atomizer. 



Pathogenicity 



The pathogenicity of Botrytis Tulipae was first demonstrated by Klebahn 

 (1905:6), who inoculated tulip bulbs with sclerotia from a pure culture. 

 However, he appears not to have done much exact inoculation work, 

 and, with the exception of the experiment cited, did not use pure cultures 

 in his infection tests. The writer does not consider that Ritzema Bos 



