Diseases of cultivated plants and Diseases of cultivated plants and trees diseasesofcultiv00massuoft Year: [1910?] 348 DISEASES OF CULTIVATED PLANTS Onion smut {UrocysHs cepulae. Frost) is only known to attack cultivated onions, and develops during the seedling stage. As a rule the first leaf shows the disease before the second leaf appears : the disease attacks the leaves in the order of their appearance. The outer coat of the bulb is P'iG. 104. — Urocystis occulta. i, upper part of rye plant diseased ; 2, spores, one of w hich has germinated and produced a cluster of secondary spores at
Diseases of cultivated plants and Diseases of cultivated plants and trees diseasesofcultiv00massuoft Year: [1910?] 348 DISEASES OF CULTIVATED PLANTS Onion smut {UrocysHs cepulae. Frost) is only known to attack cultivated onions, and develops during the seedling stage. As a rule the first leaf shows the disease before the second leaf appears : the disease attacks the leaves in the order of their appearance. The outer coat of the bulb is P'iG. 104. — Urocystis occulta. i, upper part of rye plant diseased ; 2, spores, one of w hich has germinated and produced a cluster of secondary spores at the apex of the germ-tube ; 3, a spore that has germinated and produced secondary spores, two of which have germinated. Figs 2 and 3 highly mag. also attacked. The fungus bursts through the epidermis as large, black, powdery streaks. Spore-clusters 18-25 \i diam., usually only one, brown, central, fertile cell, surrounded by many pale, sterile cells. White varieties are most susceptible to the disease. Infec- tion occurs during seedling stage by spores in the soil. It
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