398 



TEXTBOOK OF BOTANY 



Fig. 174. Longevity of embryos of seeds in Beal's experiment. 



completely satisfactory. The earlier suggestions that the change from 

 viable to non-viable seeds is the result of the oxidation of the food supply 

 and the destruction of the enzymes seem to have been adequately dis- 

 proved. Foods in seeds have been carefully analyzed and the chemical 

 changes are slight. The enzymes, on the other hand, seem to be just 

 as active as before death. Evidence against the idea that the food has 

 been completely oxidized is the dry storage of minute one-celled algal 

 spores in sealed soil samples for 30 to 40 years and their germination 

 w^hen the soils were moistened. 



Later it was suggested that death is due to the coagulation of the 

 proteins in the cells. This had in its favor the fact that there is a simi- 

 larity in the curve of longevity of seeds at high, medium, and low tem- 

 peratures and the curve of coagulation of proteins at corresponding 

 temperatures. Coagulation of proteins in cells might disrupt the organi- 

 zation of the protoplasm. Changes in the protoplasmic lipoids might like- 

 wise destroy the organization. 



A more recent answer is suggested by the discovery that the seedlings 

 derived from old seeds, from X-rayed seeds, and from heated seeds are 

 similar in survival, in growth, and in variability. Moreover, similar ir- 

 regularities in nuclear structures have been observed in microscopic 



