Peronospora infestans. Mont. Potato Peronospora

On potato stems, leaves, and tubers.
Many theories have been advanced with regard to the origin of the destructive Peronospora infestans or potato disease.
Meteorological and electrical states of the atmosphere, saturation of the plant by water, degeneration by various methods of cultivation, the ravages of insect life, these and others have each in their time been brought forward as the cause of all the mischief with our potato crops.
also liberalJy supplied n1e with siides for co1nparison.
When the potato plant has been attacked by the disease, the leaves assume a pale tint, and discolored spots appear thereon; if, in this stage of the disease, the underside of the leaf is examined it will be found to be covered with whitish patches, these patches are stems with fruit and arise from the abundant septate and branched 1nyceliu1n, or opalescent threadlike roots which grow in the midst of the cells of the leaf, and eventually appear through the stomata as fertile stems.
The eighteen at present known species of Peronospora attack parsnips, peas, onions, spinach, lettuce, clover, nettles, anemones, poppies, roses, docks, etc., but apparently not in such a destructive manner as P. infestans does with potatoes.