The Botrytis Blight of Tulips 



335 



means of camera-lucida drawings. One hundred spores were outlined 

 and the outlines measured with a millimeter rule. The error in measuring 

 was calculated to be less than 2 per cent. On the basis of these measure- 

 ments the average limits of variation may be placed at 12-24 x 10-20 fx. 



These figures do not show the dis- 

 tribution of the spores within these 

 limits. From figure 38, however, it 

 is apparent that the greater number 

 have a length of 16-17 n and a 

 width of 9-10 m- These measurements 

 were checked with those of spores 

 from another culture derived from a 

 different locality. Measurements made 

 of the spores of a large number of 

 Botrytis specimens seem to show that 

 one hundred conidia suffice to establish 

 the mode for a given species. 



The sclerotia as formed in a petri- 

 dish culture, (fig. 39) are at first white, 

 and later, a shiny black. They are cir- 

 cular, elliptical, or somewhat irregular 

 in outline, flattened vertically, and 

 often slightly convex. They might be described by the term ' ' loaf -shaped . ' ' 

 Ordinarily the sclerotia are about one millimeter in diameter. Their size 

 may be considerably affected by the amount of drying to which they are 

 subjected. 



Physiology 

 Growth 



Botrytis Tulipae grows very readily on the various kinds of media, 



both liquid and solid, on which it has been planted. In the writer's 



experimental work the commonest medium employed was potato-dextrose 



agar. On this the fungus makes a rapid, fluffy mycelial growth, which 



later becomes appressed to the surface of the agar and the sclerotia then 



begin to form. These are very numerous and are imbedded in a tough, 



mycelial membrane which covers the surface of the substratum. As 



mentioned under Conidia production, conidia are rarely formed in such 



cultures. Moreover, there is scarcely any color production in this medium. 



Fig. 37. development of conidia of 

 botrytis tulipae. x 600 



Mature conidia. (Camera-lucida drawing) 



