CHAPTER V. 



SCATTERING OF WEEDS. 



There is much to be observed as to how particular plants spread 

 from one location to another, but from the hosts of observations 

 that have been made the following means are recognized as agents 

 of conveyance to the disseminules of plants to suitable habitats. 



Physical forces: 

 Wind 

 Water 

 Snow and wind 



Animals : 



Man, furred animals and birds 



Mechanical adaptations : 

 Explosive devices 

 Hygroscopic movement 

 Burial 



In comparing the amount of seed produced by a plant with the 

 number of plants maturing from that seed, it is evident that rela- 

 tively few plants reach locations favorable to existence. Wind 

 transported fruits may be recognized by their appendages in the 

 form of wings, comas of hair and bristly parachutes. Water 

 carried fruits are characterized by lightness, inflated coverings and 

 corky buoys. Seeds disseminated by animals are characterized by 

 hooked and clawed appendages or spines which become attached to 

 pelts or fabrics or have succulent portions which are edible. Scat- 

 tering by mechanical devices is illustrated by the forcibly splitting 

 pod, the twisted pod, the spearlike fruited grasses whose twisted 

 awns aid in entering the earth and the cleistogamous flowered plant 

 which buries its seeds in the earth. 



Birds destroy large quantities of weed seeds. Mr. H. W. Hen- 

 shaw* states that a ring-necked pheasant's crop from Washington 

 contained 8,000 seeds of chickweed and a dandelion head. Birds 

 of the sparrow family, according to the same authority, feed largely 

 on the seeds of weeds. The tree sparrow consumes one-fourth ounce 

 of weed seeds per day. The tree sparrows on this basis annually 

 consume 875 tons of weed seeds in Iowa. These birds save the 

 farmers of the United States on this basis $89,260,000 annually. 



* Henry W. Henshaw. Fifty Common Birds of the Farm and Orchard. Farm- 

 ers' Bull. U. S. Dept. Agr. No. 513. 



