220 AGRICULTURAL EXPERIMENT STATION. [Jan. 



potatoes, so far as freedom from scab is concerned, is a 

 light, porous, sandy soil. On such land there may often 

 be raised, year after year, perfectly smooth crops ; while 

 on damp, heavy soil, as bad a crop may result the first 

 year as after years of continuous potato culture. At pres- 

 ent, then, we can only say that what is termed potato-scab 

 is due to the reaction of one or more of several possible 

 external irritants upon the tubers while they are growing, 

 and that the conditions which least favor its appearance 

 are those afforded by a light, open, thoroughly drained 

 soil. 



Notes. 



Damping off. — During the past fall, a few cucumber 

 seedlings in the Station greenhouse were killed by the 

 affection known as " damping off," so common and destruc- 

 tive to seedlings in the forcing bench and the hot-bed. 

 The disease, which manifests itself in the decay and conse- 

 quent falling over of the seedling stem near the level of the 

 surface of the soil, is familiar to most persons who raise 

 plants under glass. 



So far as I am aware, the cause of this trouble has not 

 been precisely investigated in this country, though it has 

 been assumed to be caused by the fungus which is known 

 to produce the same effect in Europe, Pythium de Barya- 

 nitiu Hesse. The case mentioned afforded an opportunity 

 to ascertain the correctness of this assumption. Examina- 

 tion of the stem of a fallen seedling at the point of attack 

 showed the presence of abundant fungus threads in its dis- 

 organized tissues. A piece was placed in a drop of water 

 in a moist chamber, and the threads rapidly extended 

 themselves over the glass slip which held the whole, and 

 in two days had developed the reproductive organs figured 

 in Figs. 21 to 23. These structures agree with those of P. 

 de Baryanum, as figured by Hesse, and the fungus is prob- 

 ably the same as that which produces the same results in 

 Europe. 



This fungus is closely related to the downy mildews, and 

 reproduces itself by means of zo" spores and by resting spores. 

 Fig. 21 shows two zoosporangia, and in Fig. 23 are seen 



