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germination occurs in freshly harvested or newly; threshed seeds, 

 especially after cold and moist summers. 



From the inquiries niade by various investigators on this subject, 

 it has become clear that the seeds showing this phenomenon of dormancy 

 can be arranged into two groups : — 



(1) Seeds in which the delayed germination is due to characters 

 of the embryo. Harrington (1) defines it as follows: — "Embryos 

 which, though morphologically mature, are physiologically incapable 

 of germination, even when freed from all external restrictions, until 

 fundamental changes have taken place in the embryos themselves." 



(2) Sesds in which the delayed germination is not inherent in 

 the embryos, but is due to seed coat characters, " to partial or com- 

 plete coat restrictions to embryos in themselves germinable," as 

 Harrington describes it. 



In regard to the cases in which delayed gernaination is due to characters 

 of the embryo, which must go through fundamental changes preceding 

 growth, such changes generally require considerable time, and different 

 conceptions of them exist, due to the various kinds of seeds which 

 the different investigators have made their particular study. Some 

 express themselves vaguely; for instance, Davis and Rose (2) who write 

 " the term after-ripening may be made to include the necessary proto- 

 plasmic changes, antecedent to germination, changes involving the release 

 of digestive and respiratory enzymes, this leading to rapid metabolism, 

 to embryonic changes, whether protoplasmic or metabolic." 



Others have more defined conceptions about the chief factors which 

 take part in the phenomenon of after-ripening. 



Fischer (3), Zaleski (4), Lehmann and Ottenwalder (5), Eckerson (6), 

 Harrington (7) and others bring the chemical side of the problem more 

 to the foreground. They consider embryonic after-ripening as a chemical 

 process, in which divers purely chemical changes take place, as, for 

 example, hydrolysis of the proteins, alterations in the acidity and water- 

 holding power of the embryo, metabolism of the fats, fluctuations in the 

 sugars and amide nitrogen compounds, increase of oxygen, the rendering 

 active of dormant embryonic protoplasm by (H) and (OH) ions, &c. 

 Becker (8) believes that oxygen exercises a chemical stimulus which 

 causes germination. Eckerson compares the after-ripening process with 

 common germination and states that the chemical changes during 

 the 90 days of after-ripening of Crataegus are the same as those of 

 the first eight days of germination of Ricinus. Other investigators, as 

 Detmer (9), Brown and Morris (10), Green (11), Hotter (12), Maze (13), 

 Abderhalden and Dammhahn (14), Appleman (15) and Crocker and 

 Harrington (16), consider it more as a process of ferments; for instance, 

 by the presence of peptolytic ferments, by the liberation of enzymes, by 

 the development of acidity, by increased catalase, oxydase and peroxidase- 

 activity, by increased diastatic contents, &c. The germination studies 

 dealing with chemical and enzymatical relations include a large number 

 of researches, the enumeration of which would lead me too far. 



Some ascribe the after-ripening to chemical as well as to enzymatical 

 processes. Pack (17) expresses it as follows "the changes accompanying 

 the after-ripening in Juniper seeds are represented by the accumulation 

 of cell building materials, acids, phosphatides, active reducing substances, 

 soluble sugars, pentoses, aminoacids, soluble proteins and other nitro- 

 genous cofnpounds, the accumulation of enzymes, the dispersion of 

 materials and the transformation of storage materials. This accumu- 

 lation of cell-building and cell active materials, together with the 

 culmination of enzymes, probably leads to the after-ripening of dormant 

 organs." 



Kinzel (18), Heinrioher (19) and Gassner (20) have shown that light 

 can be a factor in the protoplasm changes in delayed germination, whilst 

 Shull (21) has suggested that the character of the ovule, the origin, 



