Éléments de biologie ; un des éléments pratiques de la biologie ; un texte utile-livre de corréler la botanique, la zoologie et la physiologie humaine elementsofbiolog00hunt Année : [c1907] 166 BOTANIQUE UN périthèce ouverte pour montrer les asques. De mildiou. - Un autre groupe de champignons qui ont une importance économique considérable est composé du sac de champignons. Ces champignons sont communément appelée mildiou. Certains des spécimens obtenus plus facilement venir du lilas, rose, ou Willow. Ces champignons ne pénètrent pas dans la plante hôte à n'importe quelle profondeur, mais couvrir les feuilles de l'hôte avec l'filets blanchâtres du mycélium. Par conséquent ils peuvent b

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Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 166 BOTANY A perithecium broken open to show the asci. Mildews. — Another group of fungi that are of considerable economic importance is made up of the sac fungi. Such fungi are commonly called mildews. Some of the most easily obtained specimens come from the lilac, rose, or willow. These fungi do not penetrate the host plant to any depth, but cover the leaves of the host with the whitish threads of the mycelium. Hence they may be killed by means of applications of some fungus-killing fluid, as Bordeaux mixture.^ They obtain their food from the outer layer of cells in the leaf of the host. These mildews produce a spore-bearing portion known as a 'perithecium. When the perithecium becomes broken, a number of little sacs containing the spores are released. Each sac is called an ascus, and the spores contained within are ascospores. Each ascospore may germinate to form a new plant. Among other useful plants preyed upon by this group of fungi are the plum, cherry, and peach trees. (The diseases known as black knot and peach curl are thus caused.) Other sac fungi are the morels and truffles, the downy mildews, blue and green molds, and many other forms. One important member of this group is the tiny parasite found on rye and other grains, which gives us the drug ergot. Yeast.—Although as a group the fungi are harmful to man in the economic sense, nevertheless there are some fungi that stand in a decidedly helpful relationship to the human race. Chief of these are the yeast plants. Yeasts are found to exist in a wild state in very many parts of the world. They are found on the skins of fruits, in the soil of vineyards and orchards, in cider, beer, and other fluids, while they may exist in a dr.y state almost any^vhere in the air around us. In a cultivated state w^e find them doing our work as the agents

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