migration of weeds is an interesting one. In the East the European weeds predominate. In the Southwest and the prairie states west of the Missouri many of the troublesome weeds are indigenous to the soil. I can recall but a few troublesome weeds in Texas that have come from Europe. The Texas weeds are either of tropical origin or else indigenous. However, there are some troublesome European weeds in Texas, but they do not cover the

Fig. 33c. Distribution of some weeds. Mustard (Brassica), morning glory, etc. (C. M. King.)

landscape as they do in the North and East. The narrow leaf sneezeweed is a dominant weed everywhere throughout the state; and the buffalo bur, which is indigenous to the plains from western Texas to Colorado, is one of the dominant weeds. These weeds have largely spread since the rebellion, 1865. In the West, particularly Utah. and the mountainous countries, the scarious leaf thistle is at once a dominant species, although in places it vies with the bull thistle and in all clearings of Oregon and Washington the fireweed (Epilobium angustifolium), covers thousands of acres, while with it we may find patches

of foxglove, pansy, and a great deal of velvet grass and much Canada thistle, besides numerous other plants which are carefully cultivated in the eastern states for ornamental purposes.

Dr. Gray has somewhere said that most of the troublesome weeds of western Europe originated in the East. It is certainly true that as conditions are prepared, weeds spring into existence. Such plants as are best adapted to stand adverse conditions assert themselves and become the pests of the farmer.

Annual weeds seem to have a better chance to adapt themselves than perennial. Of the annual weeds we may mention the purslane, Jimson weed and Indian mallow.

It does not require much botanical knowledge to recognize the similarity of the flora of our "great plains." Many of the prairie plants are common from Texas to Manitoba. The compass plant (Silphium laciniatum), buffalo bur (Solanum rostratum), common sunflower (Helianthus annuus), etc., are alike common to the prairies of Texas, Kansas, Nebraska and the Dakotas.

It is remarkable how rapidly European weeds have spread in parts of South America. In the neighborhood of Buenos Ayres, are found bur clover (Medicago hispida), its allies, and a composite (Silybum marianum), which has also become noted as a pest in California; Cynara cardunculus covers the pampas for miles. The European grasses, like the perennial rye grass (Lolium perenne), squirrel grass (Hordeum murinum) and other wild barleys (H. pratense) have rapidly taken the place of native grasses. The interesting observation has been made in South America and Australia, that indigenous (native) plants have been crowded out by closely related European species. In Australia, common sow thistle (Sonchus oleraceus), a truly cosmopolitan weed, has established itself in low grounds near streams and has crowded out a native species of sonchus. It is possible that some of

our native plants are affected in this way. Common purslane (Portulaca oleracea) has without doubt in some places replaced native forms. Bull thistle (Cirsium lanceolatum) without doubt trespasses on the ground of some of our native species. C. altissimum, C. iowense and C. discolor are undoubtedly affected in this way. These thistles are certainly less abundant where bull thistle Occurs. In Manitoba the Canada thistle is much more abundant than th bull thistle. In places it occurs not only in fields, but in the woods. The sow thistle (Son

Fig. 33d. Distribution of some weeds. Canada thistle, etc. (C. M. King.)

chus arvensis) is abundant everywhere in fields. There is little of the annual species (S. oleraceus).

Most of our common weedy plants are of European origin. This is true for certain parts of the United States only, notably New York, Massachusetts, Ohio, Illinois, and other states that belong to the North Atlantic section. Yet the weeds of the interior region, the territory embracing our prairies, include a surprising number of native plants that are weedy in their nature. A few of the

European weeds are, however, great pests. Tumble weeds (Cycloloma atriplicifolium and Corispermum hyssopifolium) and ragweed (Ambrosia trifida) may be mentioned among the troublesome weeds of the West. The preponderance of these weeds is possibly due to the newness of the country, or it may be because of the plasticity of the plants themselves or on account of certain climatic conditions. In southern Atlantic states there is a surprising number of weeds that are of tropical origin. Among these are the spiny amaranth (Amaranthus spinosus), Mexican tea (Chenopodium ambrosioides), senna (Cassia occidentalis), common morning glory (Ipomoea purpurea) and I. hederacea. Quite a number have come from India, as Jimson weed (Datura Stramonium), heliotrope (Heliotropium indicum), etc. Others are European. Turning to the weeds of the Pacific coast, it may be said that its weed flora is entirely different. Dr. Hilgard, in an interesting series of articles, "The Weeds of California," in Garden and Forest, says:

"The broad fact in the premises that first strikes the newcomer in California is that a number of plants that are subjects of careful culture east of the Rocky mountains, as well as in Europe, and which quickly succumb when deprived of artificial protection there, are here among the most persistent and obnoxious weeds; while very many of those that are troublesome in the Atlantic region are conspicuously absent on the Pacific side. Radish, beet, celery, carrot, are conspicuous weeds. The smartweeds (Polygonum) are almost entirely absent on the Pacific coast. Amaranths flourish. Pusley, so troublesome in eastern states, has appeared in but few localities. As yet it has made no headway as a troublesome weed. Bur clover (Medicago denticulata), so

troublesome in South America, was one of the earliest of European introductions in California, and is a great pest." These illustrations suffice to show the differences

in the character of the weed flora in various parts of the United States.

Of the cosmopolitan weeds, shepherd's purse (Capsella Bursa-pastoris), occurs everywhere in Europe, Persia, India, Japan, United States, Chili, South Africa and Canada. Pusley occurs in India, Egypt, Europe, South Africa, Japan, China, Java and Philippine Islands; horse weed (Erigeron canadensis), everywhere in the United States from Maine to California, Brazil, South Italy, Russia, Sweden, Persia, North India, South Africa. It is sometimes a very difficult matter to decide whether plants are strictly native to a country or have been introduced, so thoroughly have they established themselves. Pusley is an excellent illustration. It is believed to be a native to the southwest.

Lines of Travel.-Weeds in their migration have followed certain well-defined lines of travel. The floras of our Atlantic states mention the occurrence of certain weeds commonly found where the ballast material was discharged. The list of ballast plants on the Atlantic and Pacific coast is constantly increasing.

In speaking of the means of transportation of weeds, Dewey says that the routes of transportation are indicated by the names, ballast plants, roadside weeds, weeds along the towpath, and railway weeds. Mr. Dewey says: "One hundred and three species were taken in ballast from Buenos Ayres to New Zealand within a period of a few years."

There is no doubt that the Crusaders brought many weeds back from western Asia into Europe. Thus plants like the horse-radish, mustard or charlock, hemp (Cannabis sativa), are Asiatic plants. Kabsch notes that most of the weeds of cereal crops like Centaurea Cyanus, Agrostemma Githago, Raphanus Raphanistrum and Myagrum sativum are foreign to Europe. But Europe has also received a number of American weeds from us, like the