DORMANCY IN SEEDS 105 



for one month before it was planted in soil. This is the desirable stratifi- 

 cation time and condition for these seeds. In conifer seeds much of the 

 stored food is in the endosperm. The difference in the growth of the 

 embryo from the low-temperature stratification and that from the non- 

 stratified seed may be explained by the movement of nutrients and acces- 

 sory foods from the endosperm during the month of stratification. Flemion 

 is planning experiments that will distinguish between nutritional effects of 

 the endosperm and possible dormancy in the embryo. 



Figure 39. Austrian pine seedlings. Left: seeds soaked for 3 days at 20° C (68° F) 

 before excising the embryo for planting. Right: seeds stratified in moist peat for one 

 month at 5° C (41° F) before excising the embryo for planting. 



The question naturally arises, What are the effective changes that occur 

 in dormant seeds with non-dormant embryos when they after-ripen in 

 low-temperature stratification? This question cannot be answered at pres- 

 ent. We have seen that both hydrolytic and oxidizing enzymes are formed 

 or activated in seeds A\dth dormant embryos, and that sugars, amino acids, 

 and other soluble organic compounds are formed from more complex and 

 less soluble compounds during low- temperature stratification. Perhaps 

 similar changes occur in seeds Avith non-dormant embryos that give the 

 embryos greater growing pressure. Low temperatures in plants in general 

 lead to the formation of soluble sugars and other soluble substances. Like- 

 wise it is possible that essential changes occur in the seed coats. We must 

 not forget also that moist stratification gives favorable conditions for the 

 leaching of inhibiting substances. In these seeds, however, like those with 

 dormant embryos, there are definite optimum temperatures for stratifica- 

 tion and the effective range of temperature is rather narrow and low. 

 Leaching ought to progress faster at high rather than at low temperatures; 

 also one might expect it to proceed over a wide range of temperatures. 



