118 GROWTH OF PLANTS 



cleaned. Giersbach found that V. nudum and V. scabrellum did not need 

 epicotyl after-ripening and offered no problem in germination. These are 

 more southerly forms. It must not be forgotten that the temperature 

 relations described in this and previous sections, as well as those to be 

 described later, probably apply to colder temperate zone plants and prob- 

 ably not to torrid zone plants unless they are high-altitude forms. The 

 species of Lilium needing low-temperature after-ripening of the epicotyl 

 after roots are formed were studied by Barton." 



In unpublished work, Flemion'has found that Chionanthus virginiana 

 and Symplocos paniadata seeds have dormant epicotyls that require low- 

 temperature after-ripening after the roots start to grow. In the first of 

 these seeds the roots grow much more promptly than in most seeds of this 

 class. In fact, many of the roots start soon after the seeds fall to the 

 ground and before winter sets in. In nature, the epicotyl will after-ripen 

 the first \Adnter and the seedling will come up the first spring. These are 

 not two-year seeds. 



In seeds that need a high -temperature period in a germinator to dispose 

 of coat resistance and a low temperature to after-ripen the embryo, we 

 noted that a constant intermediate temperature could be used that per- 

 mitted both changes to occur. The time required for both processes and 

 complete germination, however, was greatly lengthened by using this com- 

 promise, intermediate constant temperature instead of the optimum tem- 

 peratures for each individual process. No doubt in the type of seeds 

 being discussed in this section such an intermediate constant temperature 

 could be selected that would permit development of the roots followed by 

 epicotyl growth. In all these seeds temperatures as high as 10° C (50° F) 

 permit epicotyl after-ripening, and in two Viburnums even 15° C (59° F) 

 is effective. No doubt constant temperatures of 10° C (50° F) or higher 

 would permit both processes to go on. This, however, is of no importance 

 in practical horticulture, for it would greatly lengthen seedling production 

 time and it has no significance in nature, because long-maintained constant 

 temperatures do not occur in the temperate zone. 



One might question the wisdom of having seeds that produced a root 

 one year and had to wait until the next year for the epicotyl to develop 

 foliage for feeding the root. These seeds ripen in the fall and go through 

 the hazards o( one winter before even a root forms. If the roots start 

 early in the spring they draw on the stored foods all summer and no doubt 

 exhaust them before ^\'inter. The tardiness of the root formation in many 

 of these seeds probably delays root gro^vth until late summer or fall, which 

 lowers the draft on stored foods the first year. It is probal^le that a rela- 

 tively small percentage of the seeds of this group ever produce seedlings 

 in nature. This may also be true of most of the seeds of wild plants that 

 have such a complex system of after-ripening and germination. The situa- 

 tion is quite different in horticultural practice. Once one knows the tricks 

 of a given seed he can put it under the optimum conditions for each phase 



