. The fungi which cause plant disease . Plant diseases; Fungi. 142 THE FUNGI WHICH CAUSE PLANT DISEASE. Fig. 97.—Mycelium showing septation and branching. After Stevens and Hall. the host's tissue the hyphal threads are thicker, richer in proto- plasm, more septate, and much more branched and crooked than outside of the host. Aerial hyphal filaments when they touch a solid repeatedly branch in close compact fashion form- ing the attachment organs. At the exhaustion of the food supply and the consequent term- ination of the vegetative period the mycelium becomes very dense in spots and within t
. The fungi which cause plant disease . Plant diseases; Fungi. 142 THE FUNGI WHICH CAUSE PLANT DISEASE. Fig. 97.—Mycelium showing septation and branching. After Stevens and Hall. the host's tissue the hyphal threads are thicker, richer in proto- plasm, more septate, and much more branched and crooked than outside of the host. Aerial hyphal filaments when they touch a solid repeatedly branch in close compact fashion form- ing the attachment organs. At the exhaustion of the food supply and the consequent term- ination of the vegetative period the mycelium becomes very dense in spots and within these clumps of mycelium the sclerotium forms; at first white, later pink, finally smooth and black (Fig. 95). They are often found in the leaf axils (lettuce), in the pith of stems (carrot), etc. Under some conditions, as on un- suitable nutrient media, gonidia are produced. The sclerotia can ger- minate at once or remain dormant for one, perhaps several years. On ger- mination they send forth from 1 to 35'* negatively geotropic sprouts which grow to the soil surface unless that be more than about 5 cm. distant. On reaching the light the apex of the sprout begins to thicken and soon develops its apothecium; at first inverted- conidial, soon flat, and finally somewhat revo- lute. Changes in atmospheric humidity cause the discharge of ascospores in white clouds. The ascospores germinate readily but the re- sulting mycelium is of such small vigor that it is incapable of parasitism. If the ascospore germinates where it can maintain a saprophytic Fio. 98.—s. Uber- life until a vigorous mycelium is developed then piraphys^;' After the njycelium may become parasitic. Stevens and HaU. Both a^cospiores and mycelium are comparatively short-lived. The mycehum can migrate but a short distance over soil. No form of conidia except the apparently functionless gonidia is produced. The fuii^s may be cultivated easily upon ahnost any medium, com-meal-agar is especially suitable. It ha
Size: 2285px × 1094px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfungi, bookyear1913
