42 



diflii'iilly. 'I'lic author stales that seeds should eoutaiii 

 more tliau 12// water to l)e kiUed l)y tlio temperature of 

 liquid air. 



Becquerel (IDO.j) showed tliat the hig'her the de^'ree of 

 desiccation llie more resistant are the seeds to tlie tem- 

 peratures of the li(iuid gases. In a lirst series of experi- 

 ments he soaked decorticated seeds in water for 12 liours 

 and immersed them in liquid air ; the seeds did not survive 

 the treatment. On seeds dried in the vacuum at 40° for a 

 montli and immersed for 132 hours in liquid air he did not 

 observe any injury. But, out of 16 kinds of seeds, simply 

 dried in the air, 6 only survived the immersion in liijuid 

 air and these were the species which contained less water 

 (6 to 12%). In later experiments (1909), in which Bec- 

 querel intended to bring- the seeds into a state of complete 

 inactivity, he desiccated them in the presence of barium 

 oxide for 2 weeks at 35°, then put them in sealed tubes 

 evacuated to 10 * mm. of mercury, and immersed the tubes 

 in liquid air where they stayed 3 weeks and in liquid 

 hydrogen where they stayed 77 hours and, finally, he 

 maintained them sealed for 1 3^ear. When he opened the 

 tubes, the seeds germinated in the usual manner. In a 

 last experiment (1925), he used liquid helium. Seeds 

 desiccated as described above, put in a vacuum of 10 " mm. 

 of mercury and kept immersed in liquid helium at 3.8° K. 

 for 10] hours germinated like the untreated controls. 



Lipman and Lewis (1934) investigated the action of a 

 prolonged exposure of seeds to liquid air temperatures. 

 Nineteen sorts of seeds, previously dried over calcium 

 chloride and enclosed in glass tubes, were left in liquid air 

 for 30 days, in a first experiment, and for 60 days, in an- 

 other. Neither the germinating pow^er of the seeds, nor 

 their gro^vth, nor any of the characters of the plants grown 

 from them, differed from the controls. 



Lipman (1936a) immersed in liquid helium 9 kinds of 

 seeds previously desiccated for 2 weeks over sulphuric 

 acid in a partial vacuum and contained in glass tubes 1 

 cm. w4de. The temperature was 4.2° K. for about 40 hours, 



