iqiq] rose— AFTER-RIPENING AND GERMINATION 295 



results show that the oxidase activity rises with after-ripening and 

 germination. Once germination has begun, no increase is to be 

 noted. 



Discussion.— The results obtained show that the dormancy 

 exhibited by the seeds of Tilia is not due to any property of the seed 

 coat, although that structure may serve to lengthen the dormant 

 period, but is to be ascribed to conditions obtaining within the 

 endosperm or the embryo or both. In this respect Tilia resembles 

 Crataegus, and the conditions necessary for after-ripening and 

 germinating of the former are very similar to those required by the 

 latter. Even with these conditions well known and various dif- 

 ferences between dormant and after-ripened seeds clearly shown, it 

 is still impossible to define the term after-ripening in anything more 

 than general terms. The similarity of Tilia and Crataegus, with 

 respect to the conditions necessary for after-ripening, does not 

 permit one to conclude that the process in the two is the same. In 

 any case after-ripening is not to be attributed to a change in any one 

 condition, but to a series of changes which may vary for each 

 individual case. Dormancy is to be looked upon, perhaps, as a 

 condition of equilibrium in a series of chemical reactions; after- 

 ripening as a displacement of this condition. Why low tempera- 

 tures are effective in causing these changes and why the range of 

 effective temperatures is so narrow are questions still to be answered. 



Sambucus 



KiNZEL (15) states that for Sambucus nigra freezing for 2 

 winters is sufficient to bring only 39 per cent of the seeds to germina- 

 tion. Even longer freezing is necessary for the seeds 'of S. 

 racemosus. Results obtained by the writer in experiments to be 

 described are very similar to those given by Kinzel, and show that 

 in neither case have the conditions necessary for germination been 

 even approximately determined. 



Nurserymen claim that layering results in almost perfect ger- 

 mination if the seeds are not allowed to become dry between the 

 time of maturing and the time of layering. Air-dry seeds are 

 considered worthless. These statements are in a large measure 



