421 



the percentage of germination was higher in those seeds where the swell- 

 ing began later; due to the higher percentage of hard seeds. 



It was concluded from experiments with eight year old clover seed 

 which, on account of age, had already begun to grow dark, certain seeds 

 having become brown and shrivelled, and which was sorted according 

 to color, that the grains, which still had the appearance of completely fresh 

 seed, gave the highest percentage of germination. Among the slightly dis- 

 colored seeds, the brown ones germinated least and gave more than 90 per 

 cent, of rotted grains. Among these seeds, a much larger percentage of the 

 light-colored ones decayed than of tiie violet ones. This led to the deduction 

 that the violet color of the seed covering offered a protection against bac- 

 terial attack. 



The different percentages of hard-shelled seeds from a given variety 

 over a period of several years, show the dependence of that condition on 

 the weather. Hiltner, by drying the seed artificially at a temperature of 

 35°C., or over sulfuric acid, could increase the percentage of hard-shelled 

 grain. This experiment showed the atmospheric condition required to pro- 

 duce the undesired hard-shelled seeds. This condition, therefore, resembles 

 glassiness of grain. As the process of drying during ripening is hastened, 

 more hard-shelled seeds might be formed. 



In general practice, howe\er, contradictory results are often found. 

 In dry positions it was observed that the seeds of lupines, vetches, scarlet 

 clover and the kidney vetch (anthyllis) (AMndklee), in time become hard- 

 shelled, while the finer clover seeds show rather the reverse. Hiltner's 

 observation on artificially dried seeds explains this contradiction. The in- 

 fluence producing an increased toughness of the shell in thick-walled seed 

 affects thin-walled seeds as well, but in them the shell splits, consequently 

 increasing their small capacity for swelling; further Rodewald states that 

 cold can decrease the hard-shelled condition of Leguminaceae seeds. 



When one realizes that hard seeds can lie for years in the soil without 

 germinating and that those, even less capable of swelling, may germinate 

 so late that they cause a second growth, it will be evident that the seed 

 grower must control the formation of hard shells to eliminate them. In 

 the course of years, many methods have been recommended. Thus, for 

 example, the seed should be laid in a i to 2 per cent, solution of sodium 

 carbonate, to dissolve the silicic acid in the shell. Again, simply sift out 

 the hard-shelled seeds, since they are all somewhat smaller than the normal 

 ones which will germinate. Again, treating the seeds with hot water has 

 sometimes been successful, sometimes not. Dipping in boiling water for 

 one minute was injurious, but was beneficial Avhen the seed was emersed for 

 five seconds only. This treatment, however, over so short a time, cannot 

 be entrusted to laborers. Potassium permanganate, dilute sulfuric acid, an 

 ammoniacal solution of copper sulfate, have been as unsuccessful as the 

 sodium solutions. On the other hand, Hiltner found concentrated sulfuric 

 acid to be successful. The sulfuric acid injured onlv those seeds which 



