62 



As I did not try any experiments regarding the nature of the after- 

 ripening oir the changes during that period, I must refrain from giving 

 an opinion of my own about it. The delayed germination of cereals, though, 

 seems to be caused not by changes in the embryo itself, but by checking 

 influences of the seed-coat. The independence of ferments as to ripeness 

 has indeed been shown already at Wageningen by my predecessor, the late 

 Mr. F. F. Bruijning (40), who concluded that the favourable influence of 

 artificial after-ripening on the germinative power was not accompanied 

 by a rising of the feimental capacity. Wieringa, too, having done some 

 provisional tests, arrives, for the present, at the conclusion that the 

 catalase-figure of barley need not rise in consequence of the after-ripening. 

 Through want of after-ripened material these tests could not be continued. 



Literature recommends different methods to quicken the delayed 

 germination, such as^ — 



(1) Cutting the seeds or clipping them off. Hiltner (30), Crocker 

 (31a), Griiss (41), Keiszling (32), Atwood (34), and others. 



(2) Hot water treatment. Kieszling (42), Lakon (43). 



(3) Soaking the seeds in solutions of various enzymes. Crocker 

 (31a). 



(4) Addition of (H) and (OH) ions. Fischer (3). 



(5) Addition of dilute acids. Eckerson (6), Harrington (44). 



(6) Effects of light. Kinzel (18), Heinrioher (19), Gassner (20). 



I shall not dwell on the above-mentioned expedients, because they are 

 hardly ever or never employed at Wageningen. I may, however, specially 

 mention two other ways which are regularly employed with us : — 



( 1 ) Artificial after-ripening by intensive drying. 



(2) Germination at a low temperature. 



Artificial after-ripening at a raised temperature has already very often 

 been recommended, approved, and accordingly rather generally used. 

 Hiltner (30, 46), Hoffmann (35), Atterberg (46), Kieszling (32), Maz6 (38), 

 Gvimbel(47), Kidd(37), Harrington (44) and EKle (48) showed the favour- 

 able effect of drying. Mostly temperatures of 36 — -40° were recommended. 

 Hoffman supposes that the high water percentage of freshly harvested 

 seed hinders the penetration of oxygen and, because of this, at the same 

 time, the after-ripening process. When drjdng, canals and clefts are 

 formed in the seeds by their shrivelling up and the oxygen out of the air 

 is easily admitted. Hoffmann, too, considers this drying a checking of the 

 counteracting infiuences, which the absorption of oxygen suffers, caused 

 by the internal forming of carbon dioxide, as the respiration and carbonic 

 acid production are both decreased by drying. Kolkwitz (49) and Maz6 

 regard the transformation, occurring when the seeds are dried, ae an 

 evaporation of volatile stuffs, the presence of which hinders the evolution 

 of the embryo. The aldehyde, which accumulate in seeds that are not 

 after -ripened, does not, according to Maz6, kill the embryo, but it prevents 

 diastase activity and, with it, germination. According- to Kidd " redrying 

 of fully swollen seeds, which are in secondary dormancy, breaks up this 

 dormant condition and also causes acceleration of germination." 



This artificial after-ripening method by means of drying was applied 

 regularly at Wageningen until some years ago. It takes place there in a 

 double-walled drying stove (Figure I), specially made for that purpose. 

 The space between the two walls is heated by gas, till the temperature in 

 the drying space proper is 36 degrees Centigrade. A warm air-current also 

 passes through this space, previously heated by burners, causing and keep- 

 ing the right temperatiwe. By this combination of heating and conducting 

 warm dry air all through the seed, a very intensive drying is obtained 

 which often has its effect in a few daj?s, but, as a rule, in from six to eight 

 days. 



This method was always found best for rye, wheat and oats, and for 

 barley also, except in a few cases in which the time of drying had to be 

 somewhat lengthened. Under these conditions the after-ripening process 

 in barley does not apparently take place so soon, perhaps in consequence 

 of the glumes and the seed coat being tightly joined to the seed. This 



