The Botrytis Blight of Tulips 349 



mechanically injured plants. Uninjured plants were not infected. When 

 conidia were used to inoculate narcissus, there was no sign of resultant 

 injury, and microscopical examination of the epidermis showed the conidia 

 to be present but not germinated. 



Inoculation of hyacinth. — Detached hyacinth leaves were inoculated 

 with conidia from pure culture. On the fifth day after inoculation, small, 

 yellowish, depressed spots appeared. Microscopical examination of these 

 spots showed an abundance of germinated conidia but no penetration of 

 the epidermis by their germ tubes. Moreover, the tissue beneath the 

 epidermis showed no mycelium. 



Inoculation of crocus. — Slight infections were caused on mechanically 

 injured crocus leaves by mycelium of B. Tulipae, but no infection occurred 

 on uninjured leaves. A large sclerotial Botrytis from tulip caused no 

 infection in either case. Very slight infections were produced on the 

 papery scales of crocus bulbs. On injured bulbs, all the five inoculated 

 were infected; on uninjured bulbs, only one out of five was infected. 

 Microscopical sections of these lesions showed mycelium ramifying through 

 the tissue, and disintegration of the cells was observed. 



Discussion of parasitism 



It is evident from these pathogenicity experiments that B. Tulipae 

 is practically restricted to tulips. Although under certain conditions it 

 attacks some closely related plants, even such infection occurs, almost 

 invariably, only when there is an injury made at the point of inoculation. 

 Furthermore, a large number of injured plants failed to become infected. 

 When we consider the ease with which the tulip may be infected, whether 

 mycelium or conidia be used as inoculum and whether the host plant 

 be injured or uninjured, these apparent exceptions only make more evident 

 its restricted parasitism. Indeed the writer believes that in those instances 

 in which B. Tulipae is reported on other hosts, if the fungus were really 

 that species, the infection took place on an injured part of the host plant. 

 On the other hand, the pathogene shows gradation in parasitism in its 

 feeble attempts to invade plants other than its normal host. First, there 

 are plants such as the crocus, on which are produced only slight infections 

 which do not spread. Next, there are plants such as the narcissus and 

 the onion, on which the conidia do not even germinate and infection 



