6 H. H. Whetzel and John M. Arthur 



affected bulbs do send up leaves, their growth is greatly retarded. They 

 soon die and wither away, usually before they can expand, because the 

 fungus gradually rots them off underground. Initial infection evidently 

 occurs in the fall and early winter shortly after the bulbs are put out into 

 the beds, or early in the spring. Observations by the authors on the symp- 

 toms of the disease check fully with the description and illustrations of 

 them given by Klebahn (1905, figures 4-5, and 1906, figures 53-55). 



When diseased bulbs are dug up, they are found to be more or less 

 rotted, the infection beginning usually at the tip, or nose, of the bulb. 

 The roots are in most cases abundant and healthy (Plate I). The leaves 

 and the flower shoot, if they have started, are rotted, and the adjacent 

 bulb scales within are more or less involved. The rot is a dry one. the 

 tissue for a time remaining rather firm (Plate II). The healthy white 

 tissue is turned to a grayish or a reddish gray color, a very distinctive symp- 

 tom of this disease. 



On digging up the diseased bulbs, one is at once struck by the fact that 

 the soil clings tenaciously to the exterior of the rotted parts. This is 

 evidently due to the external mycelium, which binds the soil particles 

 together and holds them to the rotted bulb scales. Embedded in the soil 

 about the bulb are numerous, more or less globose, dark brown bodies, the 

 sclerotia of the pathogene. These, when dry, become almost black. They 

 vary from 1 to 9 millimeters in diameter. They are often present also in 

 large numbers on the surface of the rotted scales and neck of the bulb 

 under the adhering soil (Plate I). The sclerotia are but loosely attached 

 to the surface of the diseased tissues, and come away easily with the 

 removal of the soil. Some are occasionally to be found within the rotted 

 bulb between the decayed scales. There is an abundance of grayish 

 white mycelium on the outer surface of the bulb covering the diseased 

 parts (Plate I). Within the bulbs this mycelium frequently forms a felty 

 layer between the diseased scales (Plate II). 



ETIOLOGY 



Identity of the pathogene 



The cause of the gray bulb- rot is a fungus named by Klebahn (1905: 13) 

 Sclerotiwn tuliparum. Wakker (1885) appears to have been the first 

 investigator to discover and describe this pathogene, though he did not 

 give it a name. He, however, pointed out that it differs fundamentally 

 in many features of its structure from Peziza (Sclerotinia) bulborutn, the 

 cause of the black rot of hyacinths, which he at that time had under in- 

 vestigation. Ritzema Bos (1903 a : 182), who next investigated the disease, 

 confused the causal organism with Botrytis tulipae (Lib.) Hopkins. 4 He 



* Hopkins (1921 : 328-331) has shown Botrytis parasitica Cav. to be identical with Sclerotium tulipae Libert, 

 and has made the combination Botrytis tulipae (Lib.) Hopkins. 



