. Minnesota plant diseases. Plant diseases. 284 Minnesota Plant Diseases. The leaf underneath the spots is abnormally increased in size and distorted in shape. The pycnidia usually accompany the cluster cups and come from the same mycelium', but are gen- erally to be found on the upper surface of the leaf. They are probably male-cell receptacles which have lost their fertilizing- power and are now functionless. They illustrate a persistence of a habit after its usefulness has passed, a by no means uncommon phenomenon in f ^ ^ 1 Fig. 140.—Stem rust of wheat (Puccinia graminis). A secti
. Minnesota plant diseases. Plant diseases. 284 Minnesota Plant Diseases. The leaf underneath the spots is abnormally increased in size and distorted in shape. The pycnidia usually accompany the cluster cups and come from the same mycelium', but are gen- erally to be found on the upper surface of the leaf. They are probably male-cell receptacles which have lost their fertilizing- power and are now functionless. They illustrate a persistence of a habit after its usefulness has passed, a by no means uncommon phenomenon in f ^ ^ 1 Fig. 140.—Stem rust of wheat (Puccinia graminis). A section of such a stem as is shown in Fig. 139, highly magnified. Clusters of winter spores have broken through the skin cells of the wheat stem. The skin cells of the wheat are seen as erect chains of cells which have been thrown back by the growing out of the winter spores. Such wounds allow the water in the stems to escape since the skin cells of the wheat, which normally prevent the escape of water, are broken. Thus the wheat plants are dried up as well as starved by the drain of the parasite. Each winter spore of the fungus is seen to be two-celled. Highly magnified. Microphotograph by E. W. D. Holway. The cluster-cup is composed of a thin wall, enclosing an in- ternal mass of orange red spores. The wall splits at the summit .and opens out often in star-shaped fashion. The spores are formed in chains from the floor of the cup. The cluster-cup spores are scattered, when mature, by the wind and alight on some grass plant, where they germinate into a tube, which pene- trates into the interior of the ho-st through an air-pore, and forms. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Freeman, Edward Monroe, 1875-. Saint Paul, Minn.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplantdi, bookyear1905
