. Essentials of biology presented in problems. Biology. 174 HOW PLANTS BENEFIT AND HARM MANKIND plants from an economic standpoint are the rusts, smuts, and mil- dews which prey upon grain, corn, and other cultivated plants. Some fungi are also parasitic upon fruit and shade trees. The chestnut canker, a fungus recentlj' introduced on chestnuts planted near New York cit}', has within five years practically de- stroyed all the chestnut trees within a radius of twenty miles of the city, and is estimated to have done $10,000,000 damage already. Damage extending to hmadreds of millions of dollars
. Essentials of biology presented in problems. Biology. 174 HOW PLANTS BENEFIT AND HARM MANKIND plants from an economic standpoint are the rusts, smuts, and mil- dews which prey upon grain, corn, and other cultivated plants. Some fungi are also parasitic upon fruit and shade trees. The chestnut canker, a fungus recentlj' introduced on chestnuts planted near New York cit}', has within five years practically de- stroyed all the chestnut trees within a radius of twenty miles of the city, and is estimated to have done $10,000,000 damage already. Damage extending to hmadreds of millions of dollars is annually done by the Corn smut, a fungus parasitic on corn ; the black mass consists almost entirely of ripe spores. Wheat Rust. — Wheat rust is probably the most destructive parasitic fungus. For hundreds of years wheat rust has been the most dreaded of plant diseases, because it destroys the one harvest upon which the ci'sdlized world is most dependent. For a long time past the appear- ance of rust has been associated with the presence of barberry bushes in the neighborhood of the wheat fields. Although laws were enacted nearly two hundred years ago in New England to provide for the destruction of barberry bushes near infected wheat fields, nothing was actually known of the relation existing between the rust and the barberry until recently. It has now been proved beyond doubt that the wheat rust passes part of its life as a parasite on the barberry and from it gets to the wheat plant, where it undergoes a compUeated Hfe history. The wheat leaf, its notu:- ishment and h\'ing matter used as food by the parasite, soon dies, and no grain is produced. Some wheat rusts do not have two hosts, hving only on the wheat and wintering over by means of thick-walled spores which remain in the stubble or in the ground until the young wheat plants appear the foUowing year. Mildews. — Another group of fungi that are of considerable economic importance is made up of the sac fung
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
