METHODS OF WEED SEED MIGRATION. 7 



DISTRIBUTION OP WEED SEEDS. 



Our worst weeds are in general those which have devised the 

 most successful ways of distributing their seeds to fields and pas- 

 tures new, where the competition will not be so great as in the 

 immediate vicinity of the parent plant. Many are the methods 

 used and a number of agents or factors enter into this seed dis- 

 semination, chief among which are wind, water, birds, animals and 

 man, his machinery and methods of commerce. These different 

 methods of seed distribution should be of especial interest to the 

 farmer, for a knowledge of them will often enable him to trace the 

 source of some noxious migratory weed which has appeared upon 

 his land, and will cause him to be on the lookout for it from the 

 same or similar origin. Moreover, some of the factors of seed dis- 

 tribution are partly or wholly under his control, while others, such 

 as water and wind, are wholly beyond his power to lessen. 



SEEDS CARRIED BY WIND. The wind is one of the most potent 

 factors in the wide distribution of weed seeds. Many weeds, as 

 those of thistle, dandelion, fireweed, prickly lettuce, etc., have each 

 seed enclosed in a little case to the top of which is joined a tuft of 

 downy hairs, thus enabling them to be lifted and carried several 

 miles by the wind ; in the case of the milkweeds the tuft is attached 

 to the seed itself. Some of the grasses have long hairs upon the 

 chaff surrounding the grain, which serves the same purpose, while 

 some of the docks, the actinomeris and others have the seeds or 

 achenes winged or expanded on the sides so that they are easily 

 lifted and borne onward by a passing breeze. (Fig. 1, a and /.) 



The seeds of many weeds are blown long distances over the 

 surface of snow, ice or frozen ground. The ragweeds, velvet-leaf, 

 docks, pigweeds, chickweed and different weeds of the grass family 

 are examples of those w r hose seeds are so distributed. 



Some plants after ripening their seeds are broken off near the 

 ground and rolled over and over by the wind, the seeds dropping 

 off at intervals along the way. These "tumble-weeds" as they are 

 called, include our Indiana weeds known as old-witch grass, Rus- 

 sian thistle, two species of amaranth and the buffalo bur, besides 

 a number of others. 



SEEDS CARRIED BY WATER. Water is an important agent in the 

 dispersion of the seeds of many weeds, especially those which grow 

 in flood plains or along the banks of streams. The great ragweed, 

 smartweeds, bindweeds and others depend largely upon the an- 

 nual overflows for the wide spreading of their seeds. The seeds 



