1914] CROCKER &• DAVIS— DELAYED GERMINATION 315 



assuming that photochemical transformations are limited to the 

 embryo and are not occurring in the more highly illuminated sur- 

 rounding structures. Again, it is well established that light 

 increases the permeability of protoplasmic membranes to various 

 solutes. The possibility appears that it may likewise increase 

 the permeability of non-living semipermeable membranes of the 

 coat to oxygen or perhaps other materials needed for germination. 

 Likewise, they have failed to see that the fixation of the carbon 

 dioxide released in respiration may in some cases supply the oxygen 

 needed for germination. It is strange that these workers have 



em 



germinatrv 



demand 



most 



the conclusion is not evident. 



It is established, however, that not all cases of delayed germina- 

 tion are due to coat characters acting in conjunction with embryo 

 characters, but there are some embryos, or rather organs of some 

 embryos, that are dormant when entirely naked. But even here 

 it is probable that the explanation of the action of forcing agents 

 will not need to be veiled under such an indefinite term as stimulus. 

 Eckerson (10) has shown that the hypocotyls of haw and apple 

 seeds are dormant because of slowness in developing acidity, a 

 condition necessary for proper water absorption for growth and for 

 the formation and action of digestive and perhaps respiratory 

 enzymes. The acid development begins even during swelling in 

 all organs of most seeds, as it does in the cotyledons of the haw 

 and apple, but the hypocotyls in the latter seeds remain slightly 

 basic or neutral for a long period. It has been shown (9, 10) that 

 temperature and water and oxygen supply determine to a great 

 degree the speed of acid development in the hypocotyls mentioned. 

 Likewise, the seed coats and carpel walls play an important role 

 here, so far as they affect these factors. Acids are good forcing 

 agents for dormant hypocotyls; apparently, they have their sig- 

 nificance in this fundamental relation to water absorption and to 

 the formation and activity of enzymes. Lehmann (19) has sug- 

 gested that light and agents and conditions that substitute for 



