14 BULLETIN' 1029, U. S. DEPAETMEATT OF AGEICULTUEE. 



of the hypocotyl. In the first case invasion by the fungus takes place 

 before or during germination. In rare cases the testa remains at- 

 tached to one of the cotyledons, and delayed infection may thus occur. 

 The disease appears as shriveling of the infected tissue of the cotyle- 

 don without much loss of color, beginning usually at the margin and 

 progressing toward the petiole. Pycnidia later appear in the 

 shrunken tissue, their development being materially hastened in 

 humid environments. Infection at the base of the hypocotyl usually 

 takes place after germination, inoculum coming from the fungus 

 within the seed coat, which ordinarily remains below ground, closely 

 adjacent to the crown. In the same way nongerminable infected seeds 

 may be the source of inoculum for near-by healthy seedlings. This 

 has been shown to take place by planting such seeds alternately in the 

 furrow with healthy viable ones. In the case of hypocotyl infection, 

 the disease appears above ground as a gradual shrinkage of the suc- 

 culent tissue, progressing upward and ultimately causing a collapse 

 of the plant. As in the case of cotyledon infection, pycnidia later 

 appear in the shrunken tissue, their development likewise being en- 

 hanced by moist environment. Under greenhouse conditions where 

 a temperature of T0° to 75° F. and a relative humidity of about 60 to 

 TO per cent were maintained, the first signs of disease usually ap- 

 peared in 8 to 10 days after x^lanting, and other primary lesions con- 

 tinued to develop for three to five weeks. As a rule, cotyledon lesions 

 apjDearecl first and hypocotyl infections a few daj^s later. Out of 

 doors, where there is a greater range in environmental conditions, the 

 progress of the disease may be delayed. 



RELATION OF RAINFALL TO THE DEVELOPMENT OF THE DISEASE. 



A studj^ of the effect of variation in- the depth of rainfall on the 

 development of the disease in the seed bed was made during the 

 spring and summer of 1919 at Madison, Wis. Untreated seed of 

 the Wisconsin Hollander variety, lot No. 2-18 previously referred to, 

 was sown on May 14. A small percentage of the pods from which 

 this seed was taken had shown black-leg lesions, and in greenhouse 

 tests about 2 per cent of the seedlings had developed primary hypo- 

 cotyl infections. The seed bed was divided into four plats, which 

 were, respectively, handled as follows: Plat 1, exposed to natural 

 weather conditions; plat 2, exposed as plat 1 and sprinkled several 

 times each week during dry weather; plat 3, covered with a cold- 

 frame during rains ; plat 4, covered every evening and during rainy 

 weather. The last treatment was devised to reduce the amount of 

 dew which might form upon the plants. As a matter of fact, how- 

 ever, under the climatic conditions which prevailed during the trial, 

 this artificial inclosure led to a greater accumulation of moisture 

 upon these plants in plat 4 than upon those in plat 3. The protected 



