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The matter of the distribution of weeds is one of interest, not only to the phytogeographer, but to the farmer and horticulturist as well. Our alien flora, though Iowa is not an old state, is a large one. In 1879 Dr. Gray prepared a list of the predominant weeds of Eastern North America. In a discussion of weed migration in The Weed Flora of Iowa, I made a comparison of weeds and alien plants in Iowa. In counting the weeds of Iowa I find that 172 of that list occur in Iowa. This list can be augmented by the addition of a great many more. We are safe in saying that not far from twenty per cent of our Iowa plants are alien. Dr. Fernald states that only twenty-three per cent of the New England plants are native. In a paper which follows this, "Introduced Plants of Clear Creek Canon, Colorado,'' it will be seen that more than eighty-five per cent are indigenous. In other words, in spite of various disturbances, such as modern traffic, the burning of the forests, etc., a large per cent of species must be considered as indigenous. A few weeds like the Russian thistle, because of the xerophytic character, have been able to occupy large areas.

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Proceedings of the Iowa Academy of Science





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©1914 Iowa Academy of Science, Inc.



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