DORMANCY IN SEEDS 



119 



of after-ripening and germination and come out with a high percentage of 

 seedUng yield in minimum time, although in some cases the time is not 

 so short at that. 



Seeds Requiring Two Low-temperature Exposures. Barton '^ has made 

 an extensive study of the germination of Trillium grandiflorum seeds. The 

 following method of treating the seeds gave the highest percentage of 

 seedlings in the shortest time: the seeds were planted in pots in moist soil 

 and kept for three months at 5° C (41° F) for after-ripening; then they 

 had three months in a greenhouse, which produced a root system; then 

 five months at 5° C (41° F) to after-ripen the dormant epicotyls; and 

 finally a period in the greenhouse to grow the epicotyl and develop a com- 

 plete seedling with top and root. This means tw^o low-temperature periods 

 to after-ripen the seed and the epicotyl respectively, each followed by a 

 high-temperature period for gromng the root and finally the epicotyl. 

 This method requires 12 to 14 months to produce a high percentage of 

 seedlings. In nature the seeds would after-ripen the first ndnter, the root 

 system would grow the next summer, the epicotyl would after-ripen the 

 second winter, and the plant appear above ground the second summer. 

 This is a two-year seed in the sense the nurserymen use this term. In 

 nature, the four different periods would not be at the optimum conditions 

 a large percentage of the time either as to temperature or as to duration 

 of exposure. Consequently there must be a high wastage of seeds in 

 nature. 



Table 15. Trillium grandiflorum, 1940 Crop. Root and Shoot Production after Various 

 Temperature Treatments from Duplicate Lots of 100 Seeds Each. Planted in Soil 



in Pots. 



Table 15 shows the seedling production from various periods of tempera- 

 ture exposure. Contmuous greenhouse temperatures for 17 months gave 

 7 and 6 per cent of root gro^^i,h and 1 and per cent of epicotyl gro\\i,h. 

 Six months of greenhouse exposure followed by three months at 10° C 



