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Erigeron canadensis, the common horseweed. The Oenothera biennis became a settler of Padua, Italy, in 1812; the Erigeron canadensis near Paris in 1835. Our common rice cut grass (Leersia oryzoides), according to Buchenau, made its appearance in Italy many years ago.

The chicory was introduced near Dorchester, Mass., in 1875, and since then has spread chiefly through the northern states. The ox-eye daisy was carried to Rhode Island about 1815, and since then has spread throughout

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Fig. 34. Distribution of some weeds, quack grass, etc. (C. M. King.)

the northern states. Purslane was cultivated as early as 1672 in Massachusetts, and since then has spread to all portions of the United States. Were it not for some of

these records it would be quite impossible to say whether

a plant was indigenous or native. We have better records of the appearance of later introductions, like the golden hawkweed, first found in the eastern states, where it has become a troublesome weed and occasionally found now in the western states, even in Iowa. While some

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weeds have spread westward some of our western plants have spread eastward. Generally speaking, the movement of weeds in our own country has been westward, although niggerhead, squirrel-tail, marsh elder, and sunflower have moved eastward. In Gray’s “Manual,” sixth edition, the distribution of marsh elder is given as follows: Northwest Wisconsin to Minnesota and Kansas westward. It must, indeed, originally have been quite local in many places in this region. It is only recently that this weed has attracted attention. Another illustration is buffalo bur. In Gray’s “Snyoptical Flora,” the distribution is given as “Plains of Nebraska to Texas and Mexico.” In Gray's “Manual,” sixth edition, the statement is made, “spreading eastward to Illinois and Tennessee.” Britton, in his “Manual of Botany,” says, “On prairies, South Dakota to Texas and Mexico. Occasionally in waste places as a weed, Ontario to New Hampshire, Massachusetts and New Jersey, adventive from the West.” This plant has certainly spread to many different points in the Eastern States. The Canada thistle was early introduced in the East, but now occurs, according to Dewey, in all of the Northern states and in Canada across the continent. Its distribution shows the lines of tension in its northern extension. The same may be said of the bull thistle, which is as abundant in Montana and Utah as it is in Oregon and Washington. Where new lines of railway are opened in Canada these European immigrants follow. Few of the southern plants have spread northward. Among these, however, we may cite the horse nettle (Solanum carolinense). The record of sand brier or horse nettle forms an interesting chapter in the migration of perennial plants from one part of the country to another. It is much easier for an annual to become acclimated than a perennial. Throughout the Mississippi valley

there are tropical plants which have become thoroughly
naturalized, as Amaranthus retroflexus, A. albus, A. spino-
sus, Abutilon Theophrasti and Sida spinosa. Within the
memory of the present generation Indian mallow has
been naturalized in western Wisconsin; Argemone mer-
icana in a comparatively short time has found its way
into Kansas, Iowa and Illinois. Cardiospermum Halica-
cabum of the southwest is common in Illinois opposite St.
Louis.
Of our early weeds reliable information is often want-
ing, although in some cases the history is well known.
Prickly lettuce (Lactuca Scariola) made its appearance
in eastern Massachusetts first in 1863, but is now found
in many states of the Union, growing like a native plant.
Mention of this weed was made by Professor Arthur in an
early catalogue, but it either failed to establish itself or it
escaped the notice of botanists. In Europe, we have
reliable information concerning the spreading of a num-
ber of weeds. Water weed (Elodea canadensis), a most
harmless water plant in North America, first appeared
in Ireland in 1838; in 1846 it was recorded in Scotland;
in 1860 it was observed on the continent; in 1862, it be-
came generally distributed. Dr. Webber thinks that the
gradual lessening of this weed in Europe may have been
due to some natural enemy.
The water hyacinth (Eichornia crassipes) has become
a serious menace to navigation in Florida. This plant,
which is a native to South America, has long been culti-
vated in northern greenhouses. Dr. Webber, who made
quite an extensive study of this weed, states that it was
probably introduced into the St. John's river about 1890,
about four miles above Palatka, where it was grown in
a pond. The pond was cleared and the material thrown
into the river and from thence it spread to other streams,
having been scattered by boats. It became abundant in
1894, having been carried up the Ocklawaha River, from

h whence it was spread to all the lower streams of the St. John. Squirrel-tail grass was common about the great lakes, where it was indigenous, but was not common in many parts of Wisconsin in 1883, although, even then, it was frequently seen in low grounds about Madison, and is now abundant. It was in parts of Iowa in 1865, and now occurs in every county of the state. The hawkweed, according to Dr. Jones of Vermont, became a weedy plant between 1860 and 1875. Mr. W. H. L. Truman of Brockport, N. Y., referred to it as spreading from cultivation. It was introduced as a cultivated plant in 1818. It was recorded in Vermont in 1873, and, at about the same time, in Rhode Island. With these annuals, it is only essential that they mature their seed, but with perennials they must not only mature their seed, but the plants must be able to survive the winter. Those who hold that perennials cannot be acclimated will find an exception in Solanum carolinense, Darlington, in his “Flora Cestrica,” makes the statement that it was introduced by the late Humphrey Marshall into his botanical garden at Marshalltown. Beck, in 1833, gave its distribution as Pennsylvania to Carolina, west to Mississippi. In the second edition of Gray's “Manual,” Connecticut is included; it is also included in the fifth edition; and in the “Synoptical Flora” it is said to occur from Connecticut to Illinois and southward. Dr. Eaton, however, writes me that he has not seen it, and there is no record of its occurrence in that state, except the specimens found by Dr. Robbins. That the weed is still spreading in West Virginia is indicated by Millspaugh. In 1852, Brendel found it native in Peoria, Illinois. Solanum carolinense also occurs in Wisconsin. In recent years, many weeds have been introduced by means of impure seeds. Throughout the state of Iowa, one will find that our clover meadows contain carrot, buckhorn, chicory, evening catchfly, dock, bull thistle, sheep sorrel, and many others that might be enumerated and which have come in with impure seeds. These are treated more at length under the head of “How Seeds Are Scattered.”

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