38 MASSACHUSETTS HORTICULTURAL SOCIETY. 



been traced to the consumption of this plant in the bread made from 

 rye which was largely spurred, the result of an extremely favorable 

 season for the growth of this pernicious fungus. 



It is to be presumed that no one species of plant has caused so 

 much suffering to the human family as Peronospora investans, or 

 Potato Rot, as it is called in common parlance. Those of you old 

 enough to glance back in memory to those fatal 3'ears for Irish peas- 

 antry, when their almost sole source of sustenance was swept 

 from them by the ravages of the rot, can form an idea of the influ- 

 ence even a microscopic fungus can exert over the comfort and 

 ciAohzation of the race. The potato rot is one of those small 

 microscopic fungi best known to the naked eye hy its terrible effects. 

 Its first general appearance was in the year 1845, when it was first 

 seen in the Isle of Wight and a few weeks after was observed with 

 great wonder and dismay bj' all growers of the potato throughout 

 Europe. It is a plant which flourishes only in damp weather, and 

 its prevalence depends much on the condition of the atmosphere. 

 The fungus is first recognized by the potato leaves turning brown, 

 owing to the absorbing threads of the "rot "within the tissue. 

 Soon certain threads come to the sm'face, pass through the breath- 

 ing pores, divide into several branches, and bear the conidial spores 

 on the tips. In this condition the leaves look as if covered with a 

 fine frost. The spores thus produced germinate at once, and in 

 this way the disease is rapidly spread to other plants throughout 

 the field. The fungiis soon passes down the stem to the growing 

 tubers, and they in turn give up their siibstance to this parasite, and 

 then become rotten. As the rot does not make its appearance until 

 the hot and moist days of July, the earlier varieties stand a greater 

 chance of escaping it than the later. In all cases where the disease 

 is gradual in its appearance, and the tubers are nearly mature, they 

 should be dug at once. If the fungus has reached the tubers they 

 will rot to some extent ; but when placed in a dr}' cellar the rotting 

 is considerably retarded. In raising potatoes, select a well drained 

 or naturally dry soil ; plant early varieties and plant them early. 

 Always plant the soundest and most mature tubers. Gather the 

 crop as early as possible and burn all tops at once, thus destrojdng 

 the spores which might otherwise carry the pest over the winter 

 season. When every condition is the most favorable for its devel- 

 opment the rot will take its most violent form, and the crop will 

 fail as it has so often done in the past. 



