69 



traffic, and to some extent of lake navigation, if these may have 

 any connection with such seemingly sporadic dispersal of plants. 

 That lines of railway are important factors in plant migration, 

 especially for those of a weedy nature, is readily seen by one 

 passing along their roadbeds. But there are evidently other 

 means by which plants, whose seeds cannot be borne by currents 

 of air, are able to cross widely intervening spaces. For those 

 that grow in water or in the feeding places of migratory birds, 

 seeds lodged in their feathers or in the mud that may cling to 

 their feet is a plausible conjecture for dispersion. The trans- 

 mission of undigested seed in the alimentary canal of birds is also 

 the source of wide dispersion of plants. But when once 

 established, as in the case of this plant in the Desplaines valley, 

 which has now been under observation nearly twenty years, the 

 natural flow of the water bearing plants or seeds that may be 

 taken up by it becomes a means of the more effectual dissemi- 

 nation in a given area. A specimen collected in 1892 by Dr. 

 W. S. Moffatt on the banks of Salt Creek at Elmhurst has upon 

 the label the statement : " abundant locally, covering several 

 acres of creek-bottom." This being higher up the stream than 

 where I found it in 1890, from its abundance may have been an 

 earlier station and the source of those at Western Springs. Dr. 

 Moffatt in the same connection mentions its presence at Riverside 

 where Salt Creek enters the Desplaines River. 



The case with the third crucifer, Sisymbrium altissimum L., is 

 somewhat different, as it doubtless came into this region from the 

 northwest ; it is given as 6". Sinapistrum Crantz in Macoun's. 

 Catalogue among the additions and corrections to parts I— IV,. 

 published in connection with part IV. It had then (1890) been^ 

 " introduced in a number of places along the Canadian Pacific 

 Railway." The earliest date recorded is 1883, at Castle Moun- 

 tain, Rocky Mountains. In 1886 it is mentioned as by Lake 

 Superior; in 1889 at a station forty-five miles east of Toronto.. 

 The first authentic record I have for Chicago is an unnamed 

 specimen received from Dr. Moffatt, collected at Forest Glen, 

 1 893 ; it was soon after seen by him in the western part of the city. 

 The first place mentioned is on the Chicago, Milwaukee, and St. 



