DORMANCY IN SEEDS 



87 



in their dormancy. Indeed, one cannot determine whether the embryos 

 are dormant until they are removed and put into a germinator. The dor- 

 mancy in the embryo does not manifest itself by complete inability to 

 grow when the embryo is removed from the coats and placed in a germi- 

 nator, but rather by a marked sluggishness in early growth and by a dwarf- 

 ishness in the part of the seedling derived from the epicotyl. Once the 

 hypocotyl starts to germinate, it forms a normal vigorous root system, just 

 as does the hypocotyl of an after-ripened embryo. 



A number of investigators ^^•-''- ^^ early showed that embryos of certain 

 rosaceous seeds are dormant. They also showed that these embryos are 



Figure 27. Excised embryos of seeds of Sorbus auciiparia which had been stratified 

 for various weeks at 1° C (34° F) after three days on moist filter paper. 



after-ripened by low-temperature stratification and that the time required 

 for after-ripening the embryos in stratification is shortened if the peri- 

 carps and seed coats are removed. 



Sluggish growth of dormant embryos. It was left, however, to Flemion to 

 make a thorough-going study of the physiology of dormant embryos. 

 The sluggishness of the dormant embryo of Sorbus aucuparia ^^ is shown 

 by Fig. 26. After the excised dormant embryos have Iain on moist filter 

 papers in the light for 21 days, only the cotyledon in contact with the 

 paper has grown and become green. This indicates great resistance to the 

 movement of water through the embryo, which results in an insufficient 

 supply of water to the other cotyledon and the hypocotyl for growth. 

 Fig. 27 shows the great increase in vigor of growth of the embryo caused 

 by stratifying the intact seeds at 1° C (34° F) for two months and then 



