DORMANCY IN SEEDS 



117 



ing gave 25 per cent seedling production, which is a good yield for com- 

 mercial production but below that attained with good seeds by more fully 

 controlled inside culture. Fig. 46 shows the effect of various low tempera- 

 tures for three months on epicotyl after-ripening or shoot development of 

 three species of Viburnum.^'" For V. acerifoUum and V. dilatatum 5° and 

 10° C (41° and 50° F) are both effective temperatures for epicotyl after- 

 ripening. Viburnum prunifolium has a less limited range of temperature, 

 3° to 15° C (37° to 59° F) being effective. In this as in V. acerifoUum there 

 is a small percentage of epicotyl development without cold exposure. Also 

 it will be noted that the cold exposure period required by V. prunifolium 

 is only I5 months contrasted with 3 months for the other two. 



Figure 47. A, Viburnum acerifoUum. The effect of various planting times during 

 summer on seedling production the following spring. Left to right: Planted April 1st, 

 June 1st, September loth, 1936. B, The effect of storage on seedling production of 

 V. acerifoUum planted May 1, 1936. Left to right: Room temperature cleaned, in pulp; 

 5° C (41° F) cleaned, in pulp. 



Seedling production of the most stubborn Viburnums can be accom- 

 plished out-of-doors by early spring planting. Of course, the seedlings do 

 not come until the second spring. Fig. 47A shows the effect of planting 

 V. acerifoUum seeds at different times during the summer upon seedling 

 growth the next year. April 1 was better than June 1, and September 1 

 gave no seedlings. The earliest planting gave the slow-gro^^^ng roots 6 to 

 8 months to grow and get established before ^^^nter set in. Evidently 

 4 to 6 months, as shown by the June 1 planting, was not sufficient for many 

 of the slower gro'U'ing seeds to form roots. To avoid the hazard of two 

 \\'inters in the soil, these seeds should be spring planted. Fig. 47B shows 

 that it is better to store the seeds of this species during the Annter at 5° C 

 (41° F) than at room temperature, whether they are dried in the pulp or 



