. Fungous diseases of plants, with chapters on physiology, culture methods and technique . nt of the fungus are a considerable degree of warmth,abundant moisture, and weakened condition of the seedlings. Itis especially common when the plants are being grown in a verycrowded condition. While most common in the greenhouse, itmay affect the crop in the field as well. This fungus infests avariety of seedlings, but those of the cress, cucumber, sunflower,and others are particularly susceptible. White clover, several cru-cifers, corn and other members of the grass family are likewiseincluded among
. Fungous diseases of plants, with chapters on physiology, culture methods and technique . nt of the fungus are a considerable degree of warmth,abundant moisture, and weakened condition of the seedlings. Itis especially common when the plants are being grown in a verycrowded condition. While most common in the greenhouse, itmay affect the crop in the field as well. This fungus infests avariety of seedlings, but those of the cress, cucumber, sunflower,and others are particularly susceptible. White clover, several cru-cifers, corn and other members of the grass family are likewiseincluded among the hosts. Symptoms. The effects of this fungus may be evident uponthe seedlings a few days after germination. The point of attackis ordinarily at or near the surface of the ground. The tissuesof the affected region promptly lose their turgidity and usuallyappear water soaked (Fig. 43). When the tissues collapse theseedlings fall prostrate, and then the mycelium invades the re-mainder of the plant, if the latter is kept moist by contact withthe damp soil. 142 FUNGOUS DISEASES OF PLANTS. Fig. 43. Bean Seedlings attacked by Pythium(Photograph by H. H. Whetzel) The fungus. The myceUum, like that of most Peronosporaceae,is deUcate, more or less variable in diameter, and much branches are, for a time, at least, smaller than the parenthyphae. The protoplasm is densely granular in the growing PHYCOMYCETES 143 portions. The hyphae are apparently intercellular at first and after-wards intracellular. Terminal or intercalary spherical sporangia are sparingly pro-duced. These are usually persistent, and may be from three tofive times the diameter of the hyphae. During germination ashort tube is developed at one side, and through this the my-celium migrates, forming a kind of swarm sphere within which itbreaks up into bean-shaped masses, which are set free as zoosporeswith two lateral (Hesse figures only one) cilia. Thicker walledsporangia-like bodies, called conidia, are also
Size: 1333px × 1874px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherbostonnewyorketcgi
