LIFE SPAN OF SEEDS 55 



where the maximum amount of water is held at 10° C (50° F) with less at 

 5°, 20°, and 30° C (41°, 68°, and 86° F). It is less marked at 35 per cent 

 relative humidity. The explanation for the difference is not known. Per- 

 haps the colloidal condition, and consequently the water-holding power of 

 the seeds, varies with the temperature. Why seeds have maximum water- 

 retaining or absorbing power at 10° C (50° F), especially at high humidities, 

 is an interesting academic question for an investigator to answer in the 

 future. It is of little significance in practical seed storage. The curves in 

 Fig. 18 show again the great difference in the amount of water that differ- 

 ent kinds of seeds will hold when they are in equilibrium with the atmos- 

 phere at various humidities and temperatures. Here again the fatty seeds, 

 peanut, lettuce, flax, and pine, are relatively low in water content at all 

 temperatures and humidities as compared with tomato and onion seeds, 

 which are also fatty. 



If low water content is required for storage of seeds, how low should it 

 be? Probably the lower the better, provided the drying itself does not 

 injure the seeds. We have already seen that some seeds endure little dry- 

 ing and also, in the case of citrus, that seeds will endure more drying at 

 low temperatures with slow drying than at high temperatures with fast 

 drying. It would be well if we had data for all commercial seeds that can 

 be stored dry, on the best conditions for drying, as well as the degree to 

 which they can be dried without injury. We do not have such data, but 

 we do have enough to conclude that complete removal of water is injuri- 

 ous to most seeds and that the degree of drying endured without injury 

 varies with different seeds. Ewart -^ states that seeds will not endure dry- 

 ing below 2 to 3 per cent moisture. Waggoner ^^ dried Icicle radish seeds 

 to 0.4 per cent moisture, and Joseph ^s. se dried parsnip seeds to 0.4 per 

 cent moisture and paper birch seeds to 0.6 per cent moisture without 

 injury. Kiesselbach ^^ dried maize grains to 5 per cent moisture without 

 injury but did not find that the maximum drying endured without injury. 

 Gray birch seeds ^^ were injured by drying to 5.2 per cent moisture and 

 some pine seeds ■* are injured by over-drying. 



If we are interested in the water content necessary to keep seeds per- 

 fectly for a few years in sealed storage using other good storage conditions, 

 the answer is easy. Fatty seeds should be reduced to 4 to 5 per cent mois- 

 ture and starchy seeds to 5 to 6 per cent moisture before sealing. 



The second important storage condition affecting the life span of seeds 

 is temperature. In the case of seeds which contain so much water that 

 they soon perish at 20° or 30° C (68° or 86° F), lowering the temperature 

 to near the freezing point will prolong the life markedly. With such seeds, 

 lowering the temperature far below the freezing point may prove injurious 

 due to freezing. As the moisture is reduced, lower and lower temperatures 

 can be used, until in seeds having very low moisture the temperature of 

 liquid air is not injurious." 



Guillaumin " found that soybeans stored in air lost their vitality com- 



