MECHANICS OF DORMANCY IN SEEDS 
lOI 
their viability after 5 years in the soil, but some seeds of 8 species were 
still viable after 30 years. It is interesting to note these: Amaranthus 
retroflexus, Brassica nigra, Bursa Bursa-pastoris, Lipidum virginicum, 
Oenothera biennis, Rumex crispus, Setaria glauca, Stellaria media. 
The appearance of Stellaria media in this list is confirmatory of Peter's 
conclusions. 
The work of Duvel on the viability of buried seeds, because of 
the number and range of species represented, the planned duration of 
the project and the approach to natural conditions, is to be a notable 
work in this line. He has published^ the record of earlier tests and 
he and his co-worker, Mr. Goss, have kindly allowed me to examine 
the results of the ten-year period. Out of 105 species, representing 
25 families, more than half the species, representing more than two- 
thirds of the families, still show viable seeds ranging from i percent in 
some to nearly 100 percent in others. Of the eight species Beal finds 
retaining their viability 30 years, the six which are represented in 
Duvel's list are still viable after ten years; two of them giving about 90 
percent germination. Excepting hard forms, seeds of cultivated plants 
in general show but transient longevity in the soil in contrast to the 
rather persistent longevity of wild seeds. In general the records on 
buried seeds confirm the conclusions based on observations and on 
work of the type of Peter's. In this connection it is interesting to 
find the claims of the farmers of the South Downs, ^ that Brassica 
nigra seed can lie in the soil for years still capable of growth when 
suppHed proper conditions, confirmed by the exact work of Beal and 
Duvel. 
Theories of Longevity 
The question of the nature of the process involved in the gradual 
loss of viabiHty of seeds with the elapse of time and the effect of con- 
ditions upon the rate of this process is of first importance in a dis- 
cussion of dormancy, for they set the maximum duration of this state. 
It is well to consider first, seeds that will withstand drying and to 
consider the loss of viability in approximately air-dry condition. Two 
explanations capable of experimental investigation have been offered : 
exhaustion of stored foods and degeneration of the digestive and 
oxidizing enzym.es. ^ Both of these explanations have proved incorrect, 
6 Duvel. U. S. Dept. Agr., Bur. PI. Ind. Bull 83. 1905. 
^ Kidd. Proc. Roy. Soc. 87B: 408 and 625. 1914. 
^ Crocker and Groves. Proc. Nat. Acad. Sci. i: 152. 1915. Also unpublished 
work by the latter. 
