358 Edwin F. Hopkins 



The morphology of the parasite has been investigated in some detail. 

 The manner of formation and at + ichment of the conidia has been brought 

 out, microconidia have been demonstrated for this species and conidial 

 measurements show that while the variation in size is from 12-24 x 10-20, 

 the greater number of spores measure 16-17 x 9-10. 



Conidial production, which rarely takes place in pure cultures under 

 ordinary conditions, was found to occur abundantly when plate cultures 

 were partially dried. Abundant conidia were also formed on sterilized 

 tulip leaves in large test tubes. 



The parasitism of B. Tulipae has been fully demonstrated by numerous 

 infections brought about by the use of pure cultures of the organism. 

 Inoculations of other plants, both nearly and distantly related, while 

 showing the parasite to be restricted to tulips, show also that the parasite 

 exhibits a weak and varying degree of ability to attack other plants. 



Hibernation is by means of sclerotia which live over the winter on 

 the bulbs. Infection spreads from these bulbs to the developing shoots, 

 where abundant conidia are produced. These primary lesions serve as 

 the source of inoculum for secondary infection. The conidia produced 

 in this manner retain their vitality for several weeks. 



Sections through lesions on the bulb show an accumulation of starch 

 about the diseased area. In the penetration of the tissue by conidial 

 germ tubes, no appressoria are formed and the germ tubes penetrate 

 directly through the epidermis or through the stomata. 



Although extensive control experiments have not been made, it is recom- 

 mended that clean bulbs, careful handling of bulbs, proper storage, and 

 systematic removal and destruction of diseased plants in the field will 

 largely hold the disease in check. 



Memoir 39, The Genetic Relations of llant Colors in Maize, the sixth preceding number in this series of 

 publications, was mailed on July 19, 1921. 



