89 



any of the lists made by the writer for this paper. Since most of 

 its former stations were in exactly the same condition in 191 7 as in 

 former years, one can only conclude that the peculiar climatic 

 conditions of 1916 and 1917 are in large measure responsible for 

 its disappearance. 



Another similar case is that of Verbascum Thapstis. This plant 

 was noted in 1914 as one of the three introduced species which 

 were able to invade the aspen association successfully. In 1917 

 it was rare in the aspens, and in some particular stations where it 

 had been unusually abundant only dead flowering stems remained. 

 Its seeds are occasionally distributed by water. Seeds lodged in 

 debris on the north shore of Douglas Lake produced flowering 

 stems in 1914, and a number of rosettes were found in the vicinity 

 in 1915. Of these apparently only one came to maturity in 1916. 

 Its dead stem, with a few seeds still in the capsules, was standing 

 in 191 7, but no young plants had developed from it. 



Two colonies of Malva moschata have been known in the \icinity 

 for several years. One of these, along a roadside in clay soil, 

 still persists, while the other, growing in sand, disappeared be- 

 tween 1915 and 1917. 



The dispersal of Sedum acre is of some interest. It has escaped 

 from cultivation freely along the streets and on the vacant lots 

 of the village of Levering, five miles northwest of Douglas Lake. 

 Its seeds are probably carried from there in mud on tires or on 

 the feet of horses. At Ingliside horses are frequently cleaned or 

 watered in the lake, and the seeds are carried east and established 

 along the shore. One such colony has persisted since 191 1, and 

 another was established a mile farther on in 1916. 



From a consideration of these few species, and of the general 

 distribution of other foreign species in the region, one is impressed 

 with the precarious existence which most of these plants lead. 

 They appear or disappear, are common or rare, depending upon 

 the chance of migration and upon the yearly fluctuations of 

 climate, while the rapidity with which they migrate or increase 

 in number must be related to the great seed production so char- 

 acteristic of our introduced weeds. 



