78 FORAGE PLANTS AND THEIR CULTURE 



remained hard, which was 51.5 per cent of the whole. 

 In another series of samples from this lot, the percentages 

 which germinated after 11 months were respectively 4.5, 

 5 and 6 per cent for the different depths. 



If hard seed be scratched so that water can be absorbed 

 by the embryo, prompt germination results. Recently 

 machines have been devised for this purpose, but as their 

 capacity is small, they have been used only in experimental 

 work. 



Another method of making hard seed viable is to soak 

 the seed in commercial sulfuric acid 1 for thirty minutes, 

 and then wash with water to remove the acid. Run- 

 ning water should be used, if possible, as the mixing of the 

 acid with water engenders much heat, and if only a small 

 proportion of water is used, the seeds may be injured by 

 the heat. The seed, after washing, should be spread out 

 to dry. The acid corrodes the seed coat sufficiently so 

 that it no longer is impervious to water. 



72. Most dangerous weed seeds. The percentage of 

 weed seeds present as impurities, unless very large, is of 

 less concern than the presence of really dangerous weeds, 

 even if in very small amount. Among the most dan- 

 gerous weed seeds are the dodders, which occur in red 

 clover, alfalfa, lespedeza and rarely in other forage seeds ; 

 Canada thistle, which is not infrequent in many sorts of 

 seeds ; and quack-grass, which may be present in other 

 grass seeds. In cases where these weeds cannot be re- 

 moved by recleaning, it is usually not advisable to plant 

 the seeds. 



73. Weight of seeds. The weight of seeds to the 

 bushel varies considerably with the same species, depending 



1 Cornell Agr. Exp. Sta. Bui. No. 312. 



