52 GROWTH OF PLANTS 



mine the hardness of leguminous seed coats as well as factors that over- 

 come hardness. 



Storage of Seeds 



Conditions for storing seeds so that they will maintain their full vitality 

 for a considerable period are not only of academic interest but of great 

 economic importance. Some plants give big crops of seeds only on alter- 

 nate years, or in some cases only on occasional years, with several years 

 of poor crops between. The latter is true of red pine. Such seeds must 

 be stored so that nurseries may have an ample supply of good seeds to 

 plant every year. No doubt many seeds could be produced more cheaply 

 if a larger acreage were grown only alternate years or even less frequently. 

 Seed producers must plant sufficient acreage to supply the need for the 

 follo\ving year even when the season proves poor for production. Conse- 

 quently, in good cropping years there is a great excess of production over 

 the needs for the following year. We have been asked to determine good 

 storage conditions for Cinchona seeds so that the greater part of seeds of 

 various selections and crosses can be held viable until samples are gro\vn 

 and the quinine yield of the resulting plants determined. 



We have already discussed seeds that are ordinarily short-lived because 

 they \vill endure only slight drying in the air. Most seeds ^vill endure 

 complete drying in the air and considerable additional desiccation. What 

 are the best storage conditions for such seeds? We have noticed that the 

 seeds that live longest in seed cupboards and in the soil are of the hard- 

 coated type. Nature may give us a hint at best storage conditions for 

 seeds that stand moderate to considerable drying.- Hard coats prevent any 

 exchange of moisture and air between the outside atmosphere and the 

 living parts of the seeds. The hard coats hermetically seal the embryos 

 individually, Becquerel ^^ has determined that the percentage of water is 

 low, 2 to 5 per cent, in hard-coated seeds of legumes and of course aerobic 

 respiration is prevented except for oxygen within the coats. The storage 

 of such seeds can be made almost perfect by placing them at low tempera- 

 tures. Perhaps it might prolong the life of these hard seeds if two impos- 

 sible changes could be made in them, namely, withdrawal of the last trace 

 of oxygen and most or all of the water from A\dthin the coats. The recipe 

 for prolonging the life of seeds that endure drying is to remove as much 

 water from them as possible mthout injury, and seal them so as to hold 

 the moisture low and constant in absence of oxygen at a low temperature. 

 Let us examine the effects of these three storage factors — moisture con- 

 tent, temperature, and oxygen. 



Seeds mth soft coats stored in the air fluctuate in water content ^vith 

 the relative humidity of the air. Barton * determined the water content 

 of tomato, pine, and lettuce seeds stored open in the laboratory at Yonkers 

 eight different months of the year. Fig. 17 shows the results. During the 



