44 



BOTANICAL GAZETTE [january 



no germination, but some of the latter germinated after about 

 6 months. While exposure to - 5 C. was not sufficient to injure 

 the ungerminated seeds, it proved fatal to the germinated seeds. 

 This is due to the fact that when the coat splits open the endosperm 

 and embryo just doubles its water content and thereby dilutes the 

 cell sap to a degree which permits ice crystals to form. Seeds at 

 this period and later periods of development were killed by expos- 

 ure to - 5 C. for seven days or less. The after-ripening and gain 

 in catalase activity was a little more than enough to account for 

 the sum of the effect at 5 C. These results show that the alterna- 

 tion of temperature between -5 and 5 C. had slight forcing 

 action. This forcing action is equal to that obtained by keeping 

 seeds in running water at io° C. It is also evident that seeds ready 

 to germinate should not be subjected to -5 C. 



The early changes taking place in seeds put to germinate at 

 o=t i° C. were similar to those at 5 C. except for being retarded. 

 At this temperature the increase in catalase activity was very 

 much retarded, although it was over 3 times that gained by seeds 

 stored at -5 C. per unit time. These seeds were studied as to 

 storage material, H+ ion concentration, and permeability, and 

 found in good condition. The Juniperus seeds not only after- 

 ripened but germinated at o±i°C, even though it required 5 



or 6 months. 



Moist seeds were placed at 5 C. for germination. At this 

 temperature the catalase activity increased most rapidly. The 

 physiological changes occurring in the seed at 5 C. were most 

 rapid, and will be discussed in detail under changes preparatory to 

 germination. This constant temperature of 5 C. also gave rise 

 to by far the largest percentage of germination, and the most 

 vigorous seedlings. 



It is evident from these germination experiments that: (1) tem- 

 peratures above io° C. and below o° C. are not favorable for after- 

 ripening and germination; (2) no one of the forcing agents as 

 used was of value in germination; (3) the inclosing structures do 

 not inhibit germination; (4) but the inhibiting conditions are 

 to be found in the endosperm and embryo. These facts indicate 

 that the juniper seed has a dormant embryo that must go through 



