186 S. KLEIN 



to micro-organisms. James cites Blackman as having considered 

 that the CO2 output may be due to a purely photochemical 

 reaction, in which the organisation necessary to maintain 

 viability is destroyed, since viability is lost without any consider- 

 able depletion of seed reserves. James concludes: 'So far as 

 dormant seeds are concerned we might therefore still be up the 

 horns of the old dilemmia: either they live without respiration, 

 with extreme sluggishness no doubt, but still live, or, as Claude 

 Bernard thought, they cease to live and come alive again'. 



However, when we consider the respiration of wet seeds, we 

 are on firmer ground, since water uptake is always accompanied 

 by an increase in respiration. During the first hour of imbibition 

 there is a sharp rise in respiration, frequently with large and 

 abrupt changes of RQ, giving quite extreme values. It has 

 been shown, however, that these changes are due more to the 

 physical conditions under which the seeds are imbibed than to 

 changes in the respiratory apparatus. Later on, a more or less 

 steady trend is reached, until the time when growth processes 

 are resumed. In cases where no renewal of growth occurs, 

 respiration rate goes down with a decrease of viability in the 

 seeds^^. 



Is there any difference between the respiration rate of imbibed 

 dormant and non-dormant seeds? Let us again consider lettuce 

 seeds for illumination of this problem. Both dormant and non- 

 dormant seeds can be compared under exactly the same con- 

 ditions. The seeds are imbibed in darkness in Warburg flasks, a 

 dose of light is given after two hours to certain of the flasks and 

 readings are made. Since the first single mitotic division occurs 

 in the germinating seeds after approximately 12-14 h, only a 

 short time before the radicle protrudes through the seed coat, 

 there is ample time to look for differences between dormant and 

 non-dormant seeds during time of germination. 



The curves in Fig. 3 show hourly rates of CO2 uptake and of 

 CO2 output in seeds which were briefly illuminated 2 h after 

 imbibition. These rates are expressed as percentages of the gas 

 exchanges in these seeds which were kept all the time in the 



