WEED MIGRATION 693 



The fact, however, remains that a goodly number of our Iowa 

 weeds are indigenous to this state. Many of these were plants 

 capable of enduring sunshine and so did not have to readjust them- 

 selves to new conditions. So we have received not only from Iowa 

 but from the country to the west, as Nebraska and the Dakotas, 

 such plants as the squirrel-tail grass, buffalo bur, winged pigweed, 

 common sunflower (Helianthus annuus) , and stinkweed (Cleome 

 serrulata) . 



The same thing has occurred in states to the west where many 

 indigenous weeds are vying with the European weeds. To the 

 north in Canada a pigweed (Monolepis nuttalliana) has become ex- 

 tremely common, while such weeds as foxtail are troublesome to a 

 limited extent only. The holy grass, a curiosity in many parts of 

 Iowa, is a troublesome perennial weed of Manitoba. 



It would seem to me that it is not a question of self-fertilization 

 or plasticity but one of tolerance of weeds for sunshine and ready 

 means of dissemination either by natural agencies or by man. 



Kabsch, in a discussion of this problem, notes that precisely the 

 same things have occurred in various parts of the world where the 

 forests have been cleared. In Bolivia, Pteris, Anemia, Saururus, 

 Lilicoya were followed later by small shrubs of the Ewpatoriaceae 

 and Malvaceae. In Brazil, Pteris caudata and Tristegis glutinosa 

 make their appearance after the forest fire. In Teneriffe, in 1815, 

 Pteris, in 1820, Erica arbor.ea, and in 1830 Laurus canariensis cov- 

 ered the ground. Kabsch notes how suddenly the vegetation of 

 a forest changes in Europe when sunshine is admitted after a 

 forest fire or after the clearing of the forest. Plants like vetchling 

 (Orobus), four-leaved grass {Paris quadrifolia), Arum, lovers of 

 the shade, soon succumb, and in their places fireweed (Epilobium 

 angustifolium) , bedstraw (Galium), thistle (Cirsium), wild mar- 

 joram (Origanum), foxglove (Digitalis), and others appear to be 

 followed later by roses, brambles, hazel nut, birches, and grasses 

 like reed bent grass (Calamagrostis epigeios), meadow grass (Poo), 

 sweet vernal grass (Anthoxanthum odoratum), and bear moss 

 (Polytriclium commune) . Later shade-loving plants have a chance 

 to grow. 



In the Pacific northwest the fireweed (Epilobium angustifolium) 

 and common brake (Pteris aquilina) occupy the ground after a 

 forest fire. Velvet grass (Holcus) and groundsel (Senecio) are 

 followed by Spiraeas and the California blackberries (Bubus 

 ursvnus and B. nutkanus) which in turn are succeeded by young 



