NUMBER AND KINDS OF WEEDS ON DIFFERENT SOILS 661 



Fig. 515. A weedy cornfield, mostly Foxtail and Smartweeds. 

 (Photographed by Colburn.) 



annual sow thistle, and 10 of chickweed, besides 139 of other 

 species. He states that Korsmo's investigation revealed the pres- 

 ence of an even larger number of seeds having the power of ger- 

 mination, the seeds per square yard to a depth of 9.8 inches being 

 as follows: Fallow field, 8,682 weed seeds (over 42,000,000 per 

 acre) ; field for spring grain bearing the same crop for four suc- 

 cessive years, 28,213 weed seeds (over 136,000,000 per acre) ; fallow 

 field, 1,474 weed seeds (over 7,000,000 per acre). 



Mr. Long gives the following species of weeds found in Great 

 Britain within an area 100 feet square ; 



