The Botrytis Blight of Tulips 351 



produced successful germination. In the former there was a good develop- 

 ment of germ tubes overnight, while in the latter germination took place 

 but the development of the germ tubes was poor. This experiment 

 was conducted at room temperature. The germ tubes penetrate directly, 

 as discussed under the heading Pathological histology (page 351) and 

 cause infection. Visible evidence of infection often appears within the 

 short period of twenty-four hours, as was demonstrated in the patho- 

 genicity experiments. Under conditions unfavorable for germination the 

 conidia are able to retain their viability for some time, as the following 

 experiment illustrates. 



Tulip material abundantly covered with conidia was collected on June 

 12, 1917, at Ithaca, New York. It was kept under laboratory conditions 

 and the capacity of the conidia for germination was tested on June 12, 

 June 25, July 12, and August 2. Germination of conidia was obtained at 

 all of these dates except the last. This shows that in a dry condition 

 the conidia retain for several weeks their ability to germinate. The 

 lesions caused by their infections soon enlarge and produce more conidio- 

 phores and conidia, which in turn are capable of producing more infections. 

 That these infections are continually taking place is evident from the 

 presence of lesions of various ages on the same leaf (fig. 25). 



Conidia may be carried from badly diseased tops to the bulbs, perhaps 

 being washed down by rain. Several specimens were collected which 

 clearly showed this. Incipient lesions were found on both the stalks 

 and the bulbs of such plants, showing how the inoculum works down to 

 the bulbs. These lesions increase in size and sclerotia are produced. 

 When the bulb becomes dormant the development of the lesion is arrested 

 and the fungus is again ready for hibernation. There is no doubt that 

 the sclerotia retain their vitality for a long period. In fact, isolations 

 have been made from sclerotia which have been in a resting state for 

 several years. 



Pathological histology 



The material was fixed in Flemming's, in chromo-acetic, and in Gilson's 

 fluids, was embedded in paraffin, sectioned, and stained with both Heiden- 

 hain's iron alum-haematoxylon and Flemming's triple stain. Some 

 difficulty was experienced in sectioning lesions on the bulbs because 

 of the numerous, large, starch grains present. In order to study the 



