Pythium
(from the Greek word pytho, I cause to putrefy; plants inhabited by these Fungi soon decay). A genus of Fungi, in which are included a number of species, all of which are parasites in the interior of plants. Some of them are hurtful to certain cultivated plants. There is considerable doubt as to the actual number of distinct species of Pythium, as several are probably the same Fungus under different names; e.g., the following have been described as found in Potato plants: P. Equiseti (Sadeb.), P. incertum (Renny), P. vexans (De By.), and P. proliferum (De By.). In regard to the first three of these, Mr. W. G. Smith expresses his inability to distinguish them from one another. The genus belongs to a group of Fungi with distinct mycelium, producing sporangia at the tips of the branches, in which zoospores are produced, in the form of fragments of protoplasm, each provided with two cilia; or, rather, the zoospores are formed after the contents of the sporangia flow out into the surrounding water. On the mycelium, sexual reproduction is effected by the formation of a globular cell (the oosphere) on the end of a short branch (oogonium). Near this another small branch forms, and, growing to and piercing the oogonium, fertilises the oosphere, and produces thereby a single resting spore or oospore within it. The very nearly allied genus, Saprolegnia, differs from Pythium in the zoospores being formed inside the sporangia, and in more than one oospore being formed in each oogonium.
The food or host-plants inhabited by species of Pythium belong to widely-separated groups, including Algae, prothalli, and leafy plants of Equiseta, or Horsetails, prothalli of Ferns, and Potatoes. P. de Baryanum, a widely-distributed parasite, lives in germinating plants of Clover, Spurrey, Camelina, Maize, &c. This last species renders the lowest part of the young stems soft and tender, and soon causes decay. Its mycelium traverses all the parts that appear withered. In damp air, branches grow out, and form on the tip rounded cells, in some of which are produced zoospores, in others oospores, and on other branches conidia are formed. In whatever way formed, the spores give origin to a mycelium, which bores into suitable food-plants and reproduces the Fungus.
Remedies are hardly to be found, owing to the species of Pythium being internal parasites. Diseased plants should be removed and destroyed, to prevent the spread of these or of any other causes of disease.