the Temperature of Liquid Hydrogen on Seeds. 



863 



On July 21 he wrote to me: — "In spite of the weather I have 

 carried out my promise, and cooled some seeds in liquid hydrogen for 

 half an hour. I had to seal them up in a glass tube, cool first in 

 liquid air, and then transfer to the hydrogen. They have, therefore, 

 been cooled to - 250° C, or -252°C, while being in a vacuum 

 (seeing the air left had no appreciable tension). The seeds, in other 

 words, have been transferred to a condition resembling that of moving 

 through space. Another set of the seeds have been cooled only in 

 liquid air for comparison." 



On July 22 he added, on returning the seeds : — " There can be no 

 doubt about the seeds being cooled, as they were in the hydrogen for 

 more than an hour. In fact I used nearly 600 c.c. of liquid hydro- 

 gen." 



The seeds came to me in the small packets of tinfoil in which they 

 had been placed in the tube. On opening these it was observed that the 

 seeds were as fresh and bright as before being subjected to the treat- 

 ment. There was not the slightest discoloration observable in the 

 green tint of the peas. This practically disposed of the only anxiety 

 which Professor Dewar felt as to the success of the experiment, and 

 expressed to me on July 25 : — 



i; My own impression is that unless the sudden vacuum caused by the 

 liquid hydrogen cooling has produced physical rupture of the seeds, 

 they will germinate as usual. If they survive this awful strain, then 

 I believe no increase of the time of cooling could produce any effect 

 other than results from one hour's exposure to such severe cold." 



The seeds were sown in a cool greenhouse, without heat, on July 27. 

 On August 1 they had all germinated. In the case of the mustard, 

 136 young plants were produced from 155 seeds ; the remainder had, 

 however, germinated, but the seedlings had damped off. One of the 

 packets of wheat, for some reason, germinated slightly more slowly 

 than the rest. 



On August 5, I received a further packet of the seeds (the musk 

 excepted) indiscriminately mixed. Professor Dewar wrote the same 

 date : — " I have sent you seeds to-day which, if the treatment with 

 cold can kill, ought to be dead. They have been immersed in liquid 

 hydrogen for upwards of six hours, and no attempt was made to 

 graduate the cooling. They were placed in the vacuum vessel into 

 which the liquid hydrogen could drop from the apparatus, and had to 

 take their chance. The seeds have been soaked in liquid hydrogen, 

 and in this respect differ from the last that were cooled in a vacuum 

 from being sealed in a glass tube." 



In this instance again- the seeds did not show the smallest visible 

 trace of the ordeal to which they had been subjected. They were 

 sorted out and immediately sown, under the same conditions as before. 

 By August 9 the seeds had all germinated without exception. I com- 



