56 GROWTH OF PLANTS 



pletely in six years, while those stored in nitrogen gas or in a vacuum 

 retained their full vitality for the same period. Some other fatty seeds 

 seem especially sensitive to oxygen during storage; flax seeds, on the other 

 hand, seem to endure air storage very well. Dillman and Toole " found 

 that the latter stored in the dry air of Mandan, North Dakota, still showed 

 58 per cent germination after 18 years of storage. We have mentioned 

 other cases above where short-lived seeds were benefited by being stored 

 in absence of oxygen. In seeds with high moisture the complete removal 

 of oxygen may cause injury due to anaerobic respiration. No doubt oxygen 

 is generally injurious to long life in seed storage, but its ill effect is largely 

 overcome by proper drying of the seeds. Drying may counteract the ill 

 effects of oxygen, because dried seed coats are impervious to gases; also 

 drier protoplasm may be more resistant to whatever oxygen remains in 

 the intercellular spaces of the dried seeds. Lowering the temperature of 

 storage also minimizes the ill effects of oxygen in storage. The three 

 factors, moisture content, temperature, and oxygen, are interactive: plac- 

 ing one near the optimum lowers the ill effects of the other two that are 

 not near the optimum. 



Suppose that, as a matter of academic interest, somebody wanted to 

 find out how long the several farm and garden seeds could be kept fully 

 viable. He would have to learn the best method and the proper degree 

 of drying each, and the best temperature of storage, whether a little below 

 freezing or much lower, possibly even as near absolute zero as possible. 

 He would proceed to dry each sort of seed, hermetically seal it in a vacuum 

 or in an atmosphere free of oxygen, and to store it at the proper tempera- 

 ture. With all this his troubles would just begin. For some of the seeds, 

 at least, he would have to arrange with his great-great-grandchildren or 

 later progeny to see the end of the experiment. 



Now let us examine a few experimental results to see how much fair 

 storage conditions, probably far from optimum, will lengthen the life of 

 some short-lived seeds. 



Delphinium seeds degenerate rapidly in open air storage. Table 10 

 shows the results ^' '^ of storing annual and perennial delphinium seed 

 under various conditions. The best storage conditions used in these experi- 

 ments were probably far from optimum. These seeds were not dried be- 

 yond the drying in the laboratory in December, which gives a medium 

 low water content, as is seen in Fig. 17. The seeds were corked in small 

 vials with paraffin over the cork. This is not as good as sealing in glass 

 tubes with a flame so far as holding the moisture content is concerned. 

 Finally, the seeds were sealed in air rather than in a vacuum or in absence 

 of oxygen. In spite of only moderately good conditions, annual delphinium 

 seeds retained their full vitality in sealed storage at the 8° and 5° C (46° and 

 41° F) combination for 143 months, while in open air at room temperature 

 they had degenerated noticeably in 11 months, and nearly half had lost 

 vitality in 22 months. The perennial delphinium seeds had retained their 



