DORMANCY IN SEEDS 129 



For a long time botanists have been trying to get reliable methods for 

 determining quickly the viability of seeds without bothering to germinate 

 them. Flemion ^^ gives a review of this literature to which one may turn 

 for citations. As early as 1876 Dimitriewicz found that sections of good 

 grain seeds turned a deep rose color in sulfuric acid in five minutes, 

 whereas sections of poor seeds required 15 minutes. Lesage used dilute 

 potassium hydrate for determining viability in garden cress seeds. Heat of 

 respiration, electrical response ("blaze current"), and electrical conduc- 

 tivity have been suggested as means of quick vitality tests. Catalase con- 

 tent has been used. This offers difficulties because many dead seeds 

 contain catalase, and dead Amaranthus seeds ^^ are as rich in catalase as 

 viable seeds. Davis -^ found that soaking seeds in warm (32° C, 89° F) 

 water overnight lowered the catalase in dead seeds and increased it in live 

 seeds, and on this basis developed a viability method. This method, how- 

 ever, has been questioned as to general usefulness. Some dyes penetrate 

 dead embryos readily, but Hving embryos much less readily. Indigo car- 

 mine 1:2000 is the best dye for this purpose. Several chemicals enter the 

 seeds and are reduced by the respiratory activity of seeds producing color 

 reduction products. Soaking seeds in solutions of para- or ortho-dinitro- 

 benzene for 20 hours, followed by treatment with ammonia for one hour, 

 gives an orange coloration in live seeds. Tellurites, tellurates, selenites, 

 and selenates enter seeds and are reduced to the elements tellurium and 

 selenium, giving purple color with the former and yellow with the latter. 

 Tetrazolium salts " have been very recently recommended as substitutes 

 for selenium salts because they are less toxic. They are reduced to red 

 formazanes. 



In three papers '^' ^''' '*- Flemion describes in detail the methods of excis- 

 ing embryos and of running the viability tests on 38 different species of 

 plants representing 10 different families. In later unpublished w^ork she 

 has extended this method to 15 other species of dormant seeds represent- 

 mg 3 additional families. In some of the seeds, excising of the embryo 

 without injury is a fairly difficult process and requires considerable tech- 

 nical skill. This is especially true of Symphoricarpos, which has a tough, 

 leathery coat and a rudimentary embryo embedded in the endosperm. A 

 quick vitality test on this seed not only requires much work but 6 weeks 

 to get results. This seed represents an extreme case and is of no practical 

 significance. In most seeds of practical interest the excising of the embryo 

 is relatively simple; and the period for running the viability tests ranges 

 from 3 to 14 days, about the time required for germination tests of farm 

 and garden seeds. In all cases, Flemion finds that viability tests deter- 

 mined with excised embryos check closely with germination obtained by 

 after-ripening the dormant seeds and later germinating them. Even the 

 relative vigor of the several embryos is clearly sho^vn, as it is with the 

 speed of germination of the after-ripened seeds. 



