96 P. F. Wareing and T. A. VilUers 



drin, there is an associated decrease in the level of the endogenous 

 inhibitors. Various workers have since investigated the changes in 

 inhibitor content of buds during chilling, and most of these have con- 

 firmed that the inhibitor level gradually decreases during the winter, 

 reaching a minimum in the spring when the buds are expanding (5, 

 9, 15). Phillips and Wareing (20) investigated the changes in inhibi- 

 tor level of buds of Acer pseudoplatanus throughout the year and ob- 

 served that the amount of inhibitor gradually increased in develop- 

 ing buds in the late summer, reaching a maximum in October. The 

 inhibitor level decreased gradually during the winter, reaching a min- 

 imum in April when the buds were expanding. There is no doubt, 

 therefore, that in this species there is a marked annual variation in 

 inhibitor level which is correlated with the state of dormancy of the 

 buds. Such a correlation does not, of course, necessarily imply a 

 causal relationship, and studies of this sort on tree buds imder natural 

 conditions do not readily lend themselves to experimental techniques 

 designed to elucidate whether the changes in inhibitor level control 

 the changes in states of dormancy. For this latter purpose, seeds are 

 much more suitable objects of study since they can readily be main- 

 tained under controlled conditions and can be more easily exposed 

 to various chemical and other treatments. 



Studies on changes of inhibitor levels in seeds in response to chill- 

 ing have been very few. Barton and Solt (3) and Luckwill (19) ob- 

 served some reduction in the inhibitor content of seeds of Sorbus au- 

 cuparia and apple, respectively, in response to chilling. Lasheen and 

 Blackhurst (18) observed that ether-soluble inhibitors disappeared 

 from seeds of Rubiis during chilling, and the disappearance of the 

 inhibitor was correlated with the breaking of dormancy and ability 

 of the seeds to germinate. On the other hand, there was little corre- 

 lation between the inhibitor content of the embryos and (heir state 

 of dormancy. Several workers have studied dormancy in seeds of Frax- 

 inus in relation to inhibitors. Ferenczy (8), using crude extracts of 

 the various parts of the fruit of F. excelsior, concluded that most of 

 the inhibitory material is present in a mucilaginous layer surroimd- 

 ing the seeds. He found a decrease in this inhibitory material during 

 moist storage at both 20° and 5° C. Using ether and aqueous ex- 

 tracts of F. spaetliiana, Asakawa (1) found that there was some in- 

 hibitory activity in the pericarps, but little in the seeds. The peri- 

 carp inhibitors decreased during moist storage at both 2° C. and lab- 

 oratory temperatures, probably by leaching. 



Studies With Seed of Fraxinus excelsior 



During the past 3 years we have carried out a detailed study of 

 doiniaucy in seeds of F. excelsior, particularly in relation to growth 



