62 GROWTH OF PLANTS 



of the extract. Seeds grown on the meal of the old seeds were more in- 

 hibited than seeds grown on the extract. The inhibition on meal was so 

 great that many of the embryos of the fresh seeds could not free them- 

 selves from the seed coats. This work suggests that we need to examine 

 aging seeds of many sorts of plants to learn whether accumulation of 

 inhibiting or toxic substances increases with age and leads to degenera- 

 tion, or whether Schwemmle's findings apply to the particular seeds he 

 studied due in part to their hybrid natiu-e. If accumulation of metabolic 

 products leads to the death of long-stored seeds, the good storage condi- 

 tions are those that reduce the rate of formation and accumulation of such 

 products. Undoubtedly low moisture content and low temperatures will 

 fulfill these conditions. Perhaps many seeds last longer soaked up in the 

 soil than they do in dry storage, either because such intermediate products 

 are not formed in imbibed seeds or because they diffuse out through the 

 soil water. 



The later work indicates that the fall in the vitality of seeds in dry 

 storage is due to a gradual degeneration of the nuclei ^' of the cells of the 

 embryo, which results in disorder in the delicate mechanism of mitotic 

 division. This work shows that aging, heating, and x-ray treatment of 

 dry seeds all cause a similar degeneration.. Seeds partially injured by any 

 one of these conditions produce seedlings showing an increased number of 

 irregularities in chromosome distribution during mitosis, chromosome muta- 

 tion, and an increasing number of mutants in the resulting plants. Nava- 

 shin " found that fresh Crepis lectorum seeds produced plants in which 

 only 0.1 per cent showed chromosome irregularities in mitosis, and a cor- 

 responding percentage of mutants among the plants. On the other hand, 

 more than 80 per cent of the plants grown from five-year-old seeds showed 

 cytological mutations in the roots, and the seedlings grown from such 

 seeds showed many abnormalities. Many of the plants died before they 

 were large enough for transplanting, and others at later stages. Many 

 albino plants appeared. Some of those that reached maturity were par- 

 tially or wholly sterile. Peto " has found similar changes in plants produced 

 from old maize grains, as well as in plants produced from barley grains 

 subjected to high temperatures. By heat treatment he produced a tetra- 

 ploid barley plant. Avery and Blakeslee ^ find that Datura seeds mutate 

 much more slowly when buried in the soil than when stored in the labora- 

 tory, just as they degenerate much more slowly, as mentioned above. In 

 a summary of the literature, Goodspeed '^ shows that irradiation of plants 

 causes chromosome and plant mutations very similar to those produced 

 in seeds by aging or heat treatment. 



The literature is accumulating rapidly on the chromosome and plant 

 mutations caused by aging, heating, and irradiating of seeds, and the 

 results are in general agreement. Let us summarize briefly the effects 

 these treatments produce, realizing of course that the degree of change 

 increases with the aging under a given set of storage conditions or with 



