DORMANCY IN SEEDS 131 



What are the relative merits of viabihty tests based on color reactions 

 and those using excised embryos? The color reaction requires only 24 to 

 48 hours, whereas the excised method requires 4 to 14 days. In both cases 

 the embryos must be at least partially removed, but for the color tests 

 less care needs to be taken against injuring the embryo. Finally, Flemion 

 claims that the main advantage of the excised embryo method is its relia- 

 bility. Often worthless embryos show considerable color with the color 

 tests. In the excised embryo method the embryo shows its viability by a 

 growth reaction of some sort. It is a direct viability test. 



Let us select two of many cases where the excised embryo method was 

 applied to practice. A seedsman reported that he had a chance to pur- 

 chase 2000 bushels of Douglas fir cones that had been found in a squirrel 

 cache. The seeds looked good, but a test for viability was desired; also 

 the offer had to be accepted in a few days, whereas an ordinary germina- 

 tion test required about 60 days. Within 5 days by the use of this quick 

 viability test Flemion was able to advise that 95 per cent of the seeds were 

 dead and the other 5 per cent showed very low vitality. The largest dis- 

 tiller of witch hazel has always used wild growth as the source of wood 

 for distillation. This source became scarce and had to be gathered at 

 greater and greater distances from the still. A few years ago the distiller 

 decided to start a grove near the still as a wood source. A quick vitality 

 test showed that the peck of seeds they had for this purpose was entirely 

 dead. The collection of seeds the next autumn proved viable and was 

 after-ripened with three months of stratification at 5° C (41° F). Several 

 hundred thousand seedlings are now ready to transplant into' the proposed 

 grove. 



The excised embryo test for viability of dormant horticultural and for- 

 est seeds is used extensively at Boyce Thompson Institute, and is gradu- 

 ally being adopted by seed-testing laboratories. 



Chemicals as Forcing Agents for Dormant Seeds 



As we shall see in a later chapter, Denny and co-workers have been 

 very successful in forcing dormant buds with chemicals. Among the 

 chemicals tested to date, few have proved successful in forcing dormant 

 seeds. Nitrogen compounds for light-favored seeds and concentrated 

 sulfuric acid for hard seeds and seeds with resistant coats are notable 

 exceptions. The latter, however, is a corrosive action. A few kinds of 

 dormant seeds are forced by one or more of the following substances: 

 carbon dioxide, mercury salts, hydrogen peroxide, anesthetics, etc., but 

 none of these is generally effective as a forcing agent. We have tried bud- 

 forcing chemicals, hormones, and other compounds, on both dormant 

 seeds and embryos, without promising results either in forcing the dormant 

 seeds to germinate or dormant embryos to grow with vigor. It is possible, 

 however, that later researches \vill find chemicals that will parallel tem- 

 perature manipulations in eliminating seed and embryo dormancy. 



