192 A. M. MAYER 



will not germinate without awaiting some indicative external 

 sign, usually the protrusion of either the radicle or plumule from 

 the seed coat, and by the time this has occurred germination has 

 been completed. No other clear indication of whether germina- 

 tion will or will not occur has been found for any seeds. Bio- 

 chemical tests or histochemical staining have not proved ade- 

 quate to answer this question. 



The two treatments of the seeds which we will now consider 

 are using thiourea, which breaks dormancy, and coumarin, 

 which is a germination inhibitor and in fact induces dormancy. 

 The results to be considered, primarily those of Dr. Poljakoflf- 

 Mayber and myself, are concerned with the biochemical changes 

 which occur in lettuce seeds germinated in solutions of these two 

 substances, as compared with those of seeds germinated in water. 

 It may be said at the outset that in no case is there any certainty 

 that these changes are in fact directly related to the dormancy- 

 inducing or -breaking action of the chemicals concerned; in 

 some cases, however, they are suggestive of this. 



During germination of seeds there is a general activation of 

 all the enzyme systems in the seeds, due to water uptake. This 

 activation is accompanied by a breakdown of certain storage 

 products within the seeds, and by a general increase in the 

 oxygen uptake. However, not all enzyme systems increase their 

 activity at an equal rate and a few of them in fact rapidly 

 decrease in activity as germination proceeds. Studies of the 

 biochemical changes occurring in the germinating seeds have not 

 yet been extended to all the metabolic processes that occur. 

 Certain vital systems have not as yet been studied at all, whereas 

 others have been shown to be of only secondary importance. It 

 is therefore intended to confine the discussion to the breakdown 

 of certain storage materials and to the possible oxidative path- 

 way occurring during germination. 



It became clear fairly early in the investigation that in lettuce 

 seeds the first substrate to be used during germination is the 

 small amount of sucrose present^. The breakdown of this 

 sucrose is not inhibited by either coumarin or thiourea during 



