CHAPTER IX. 



WEED MIGRATION. 



Geographical botany is that phase of botany which concerns itself 

 with the distribution of plants over the earth 's surface. The study 

 involves questions of geology, climatology, plant physiology, geog- 

 raphy, paleobotany, ethnology, history, agriculture, horticulture 

 and commerce. J. Burtt Davy says: "The facies of the world's 

 flora is rapidly changing, and tends to become more uniform, within 

 certain limits, under the influence of agriculture !and commerce." 

 Before the advent of man the chief factors in weed immigration 

 were the wind, water, snow, animals of various kinds, e. g., birds, 

 mammals, reptiles, insects and gravity. Primitive man must have 

 been an important factor in the distribution of plants. Many 

 plants were no doubt widely scattered by the Indian. Some, like 

 the persimmon, plum, pawpaw, maize; etc., were cultivated; but 

 many weeds also were scattered by the Indian, finding a congenial 

 environment near the wigwams. Commerce and the quest for new 

 lands distributed many species far and wide. Lists of weedy plants 

 of every civilized country, as indicated by Fernald, Davy, Gray 

 and other botanists, show that a large percentage are foreigners. 

 With the rapidity of modern transportation and with communica- 

 tion with every part of the world, weed seeds have naturally been 

 carried with the commercial products. Without exception, wherever 

 agriculture has advanced in Iowa, I believe weeds have followed 

 cultivation, generally making their appearance along the water 

 courses where our agriculture was fostered earlier than in the in- 

 terior of the state. For instance, such weeds as Jimson weed, 

 Indian mallow, burdock, mayweed or dog fennel, cheeses, mullein, 

 dock, black nightshade, smartweed, bull thistle, pigweed, lamb's 

 quarters, and purslane, have been known in Iowa ior more than 

 sixty years. Some of these were abundant species in cities and on 

 farms along the Mississippi long before central and northwestern 

 Iowa became settled. There are regions in northwestern Iowa 

 where some of the above weeds are still unknown. The mayweed, 

 velvet weed and mullein were only infrequent weeds in central 

 Iowa twenty-five years ago, though becoming more frequent from 



