794 Journal of Agricultural Research vol. vi, no. 20 



CONCLUSION 



By "impermeable seeds" is meant those seeds all parts of whose seed 

 coats are impermeable to water at temperatures favorable for germination. 



It is impossible to distinguish between impermeable and permeable 

 seeds except by testing their ability to absorb water at a temperature 

 favorable for germination. 



The production of impermeable seeds is particularly characteristic of 

 the Leguminosae, but it occurs also in many other plant families. 



Among the cultivated species which sometimes produce impermeable 

 seeds are okra, hollyhock, alfilaria, atriplex, asparagus, morning-glory, 

 canna, cherry tomato, and nearly all of the cultivated species of Legumi- 

 nosae. 



Impermeable seeds frequently retain their vitality for many years, 

 sometimes for at least as many as 80 years. 



Fresh impermeable seeds germinate promptly when the seed coat is 

 broken or becomes permeable. 



The viability of fresh impermeable seeds is frequently greater than the 

 viability of fresh seeds of the same species which are permeable. 



Seeds of the common clovers, alfalfa, and hairy vetch which are im- 

 permeable at the end of three to five years under laboratory conditions 

 of storage retain their vitality apparently unimpaired up to that time. 

 The viability of the permeable seeds in the same lots decreases slightly 

 in the second and third year and more in subsequent years. 



In dry storage nearly all impermeable alsike-clover, white-clover, and 

 sweet-clover seeds remain impermeable until at least 2 or 3 years old. 

 Impermeable red-clover seeds become permeable gradually in dry 

 storage, but from one-third to two-thirds of them may still be imperme- 

 able after four years. The majority of impermeable alfalfa and hairy- 

 vetch seeds become permeable before they are 2 years old. Okra 

 seeds become less permeable as their age increases. 



In wet blotters nearly all impermeable alfalfa, crimson-clover, hairy- 

 vetch, and okra seeds soften and germinate in one year, though a very 

 few may remain impermeable even after three or four years. Imperme- 

 able seeds of red clover, alsike clover, white clover, and sweet clover 

 soften and germinate more slowly, but with no uniformity as to rate. 

 All germinate within one year in some cases, while in other cases over 

 50 per cent are still impermeable after four years. 



Impermeable clover seeds which were thoroughly matured before 

 harvesting soften and germinate more slowly under conditions favorable 

 for germination than do impermeable seeds of the same species which 

 were less well matured; they also become permeable more slowly in dry 

 storage. 



Impermeable seeds become permeable more rapidly in wet blotters 

 than in dry storage. 



