1909.] 



Latent Life of Resting Seeds. 



429 



The Effect of Extremes of Temperature on the Germ/mating Power and 

 Enzyme Contents of Seeds. 



Sigh Temperatures. — All the enzymes present in the resting grains are 

 completely destroyed by moist heat at 100° C, and the same is true of the 

 germinating power of the grains, no signs of germination being apparent 

 in the seeds of cereals which have been immersed in boiling water for a few 

 minutes. This appeared to suggest the possibility of some co-relation existing 

 between the germinating power and enzyme reaction of seeds regarding their 

 powers of resisting high temperatures, irrespective of the fact that no such 

 co-relation exists between these two phenomena as regards their capacity for 

 withstanding time. 



To test whether any such connection really exists, many experiments were 

 carried out, using dry instead of moist heat. 



It is important that the seeds should be as nearly completely dry as 

 possible, a,nd for this reason before being used for an experiment they were 

 taken from the store room, which was the driest place obtainable, and placed 

 in sulphuric acid desiccators kept in an oven at about 35° C. for a week or 

 more. The first series of experiments was carried out at 100° C, and the 

 method adopted was as follows : — The dried grains were placed in perfectly 

 dry test-tubes, which were fitted into holes in a sheet of cardboard. The test- 

 tubes containing the seeds were placed in a vessel containing boiling salt 

 solution, and the bulb of a thermometer was put into one of the test-tubes 

 among the seeds. The sheet of cardboard prevented any steam reaching the 

 open ends of the test-tubes, so that the grains were kept perfectly dry. The 

 grains were kept at a temperature of 99° to 100° C, for different intervals 

 of time varying from \ hour to 16 hours, and on removal from the test-tubes 

 their germination capacity and enzyme reactions were investigated. The 

 results of these investigations may be obtained in detail from the following 

 tables. 



The germinating power became gradually weakened as the interval of time 

 during which the grains were subjected to this high temperature increased, 

 but the same did not apply to the enzymic activity, for after 16 hours' 

 exposure to 99° or 100° C. the actions of the enzymes were apparently in 

 no wise impaired. 



A different method had to be adopted in order to raise the temperature of 

 the grains above 100° C. This was done by spreading the seeds, which had 

 been previously dried in the desiccator, as before in a single layer, and placing 

 them in an oven heated to the required temperature. The temperature 

 of the oven was first raised to 120° C. and kept constant for an hour. The 



