112 



GROWTH OF PLANTS 



period; and the length of time for concentrated sulfuric acid treatment 

 if it is used to overcome the coat resistance. 



Table 13. Effective Pretreatment for Seeds Requiring Periods at Both High and Low 

 Temperatures before Planting in the Greenhouse. 



* Give some germination with pretreatment at low temperature only but much better 

 with high plus low. 



t Neither high temperature nor H2SO4 alone sufficient to overcome coat effect. Best 

 results when these two treatments were used together. 



t Effective length of treatment depends on whether entire nutlet stones, stone pieces, 

 or single seeds are used. 



One should realize that there is no hard-and-fast line between seeds of 

 this class and those of the previous class. Seeds with only moderately 

 resistant coats may respond fairly well to simple low-temperature stratifi- 

 cation; yet they give a higher percentage of seedlings if first exposed for 

 a period to a high temperature in the soil, followed by low-temperature 

 stratification. This is true of Rhodotypos kerrioides seeds. 



Pfeiffer has sho^vn beyond doubt that organisms in the soil decompose 

 the non-dehiscent coats of Symphoricarpos seeds. We have assumed that 

 organisms decompose the coats with dehiscent lines at these lines. This, 

 however, is questioned by some workers. Miiller ^^ claims that seed coats 

 with dehiscent lines are weakened at these lines only by water absorption 

 and not by soil organisms, acids, and other agents unless these lines (planes) 

 are composed in part or wholly of cellulosic materials. In this group of 

 seeds the fact that the coat resistance is overcome only at higher tempera- 

 tures that permit action of microorganisms is evidence against Miiller's 

 conclusion. 



