. Journal of agricultural research . lant from X to iinch below the ground level. Early infection is at first manifested bydeep brown lesions. At this stage the host exhibits a slight wilting, asthough suffering from a lack of water in the soil. Soon after, however,the lesions become covered with white radiating mycelium which en-circles the foot of the plant. At this stage the epidermis and the cam-bium become water-soaked but remain firm, the foliage droops, loses itsgreen color, and the plant never revives. The fungus seldom works toany considerable extent upward on the main stem; but it al
. Journal of agricultural research . lant from X to iinch below the ground level. Early infection is at first manifested bydeep brown lesions. At this stage the host exhibits a slight wilting, asthough suffering from a lack of water in the soil. Soon after, however,the lesions become covered with white radiating mycelium which en-circles the foot of the plant. At this stage the epidermis and the cam-bium become water-soaked but remain firm, the foliage droops, loses itsgreen color, and the plant never revives. The fungus seldom works toany considerable extent upward on the main stem; but it always worksdownward toward the main root and rootlets, especially those whichare nearest to the surface. If a dead plant is pulled out, its roots and134793°—19 2 134 Journal of Agricultural Research voi. xviit. no. 3 rootlets are usually found covered with a white weft of the mycelium ofthe causal fungus. If the soil is kept moist and the dead plant remainsuntouched, the fungus will grow out on the surface of the soil in radiating. Fig. I.—a, intracellular nature of Sderotium rolfsii hyphae in cantaloupe tissue; B and C, manner inwhich the fungus pierces host cells; D, E, and F, method of budding and formation of new mycelialgrowth; G, manner of growth of mycelium, forming strands; H, dissolved middle lamellae of host cells. fans around the foot of the dead plant (PL 6, A). With sweet potatoesin the seed bed the fungus often attacks young sprouts as soon as growthstarts, in which case the mycelial strands work their way upward and Nov. 1,1919 Recent Studies on Sclerotium rolfsii Sacc. 135 invade the entire tender stems (PI. 5, A), which soften considerably andbecome covered with minute sclerotia. The fungus then works down-ward and rots the mother sweet potato. With stored cabbage the rotis confined to the two outermost layers of the head, which blacken andturn soft (PI. 4, A). MANNER OF GROWTH The fungus was first studied by Halsted (d) and later by others, who,however, di
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