SOME ASPECTS OF PERIODICITY IN PLANTS 65 



in poisonous alcoholic solutions, including absolute alcohol 

 and corrosive sublimate. He showed that seeds (especially 

 those of Medicago sativd) could live in these poisonous sur- 

 roundings during the whole time of his experiment, namely 

 fifteen to sixteen years, but that even small traces of water led 

 to the death of the seeds. These experiments prove, on the one 

 hand, that dry seed-coats may be impervious to dry gases and 

 to alcoholic solutions ; on the other, that seeds can live for years 

 under conditions that almost or entirely exclude respiration 



Mortality of seeds of Scots pine. 



(except in the form of infinitesimal intramolecular respiration)- 

 Likewise interesting were the observations of P. Becquerel, who 

 found that various kinds of seeds, belonging to fifty species, had 

 retained their vitality after having been kept in a museum during 

 twenty-five to eighty-five years. He showed that these long-lived 

 seeds had one character in common, namely an impervious, even 

 stony, covering. P. Becquerel also found that when the seed- 

 coat of a dried seed was artificially perforated and the seed was 

 subsequently kept in high vacuo for two years it preserved its 

 vitality. These various observations suggest that the death of 

 seeds exposed to the air is due to access of water and oxygen. 



