The Botrytis Blight of Tulips 



353 



The mycelium in the bulbous 

 tissue is usually of small diame- 

 ter and is both inter- and in- 

 tracellular. Usually in that 

 part of the tissue where the 

 mycelium is advancing and 

 the cells are not yet killed, it 

 is intercellular, while in the 

 older part of the lesion the 

 hyphae penetrate into the cells 

 as well as between them. The 

 protoplasm of the cells at this 

 stage is practically gone. The 

 collapse of these empty cells 

 causes the lesion to be de- 

 pressed. Sclerotia sometimes 

 form on the surface of the 

 lesion. In figure 43 an incip- 

 ient sclerotium may be seen. 



Fig. 44. 



STARCH ACCUMULATION 

 TISSUE. X 277 



IN DISEASED 



Fig. 4.5. healthy bulb tissue. X 277 ] 



The amount of starch shown here may be 

 compared with that shown in figure 44 



Starch cells in a diseased area of an outer bulb 

 scale, showing numerous starch grains and 

 intercellular mycelium. (Camera-lucida drawing) 



Vascular bundles in the bulb 

 scale were markedly affected, and 

 in one case the xylem had entirely 

 disappeared while the phloem, 

 though attacked, still remained 

 in part. In another specimen the 

 bundle had been disintegrated on 

 the side toward the lesion. This 

 involved the phloem, the cells of 

 which stained a deeper blue. 

 There was starch accumulation in 

 this region. 



Penetration of the fungus into 

 the leaf tissue has been observed. 

 No appressoria are formed by the 

 germ tubes, which instead pene- 

 trate directly through the leaf 

 surface, either through stomata or 



