26 MISC. PUBLICATION 434, U. S. DEPARTMENT OF AGRICULTURE 



against drying out or heating. The medium and seed are separated 

 before sowing largely to make the seed easier to handle in drill sowers. 

 When the seed is larger than the particles of the stratifying medium, 

 separation is successfully accomplished by shaking the mixture over 

 wire-mesh screens or washing it through the screens. When the seed 

 are small and about the same size as the medium, difficulty is en- 

 countered in attempting to separate the two, and it may be necessary 

 to sow the seed by hand without separating it from the stratifying 

 medium. Sowing unseparated seed by hand may be advisable on 

 other occasions also, since no mechanical seeder has been developed 

 that is suitable for sowing all deciduous species. In these instances, a 

 knowledge of relative weights of stratifying medium and seed will aid 

 in determining how much of the mixture to sow per lineal foot of row 

 for the desired density. 



ACID SCARIFICATION 



Acid scarification, or a method by which impermeable seed coats 

 are etched or pitted by acid, succeeds best and is preferred practice 

 on such leguminous species as honeylocust, black locust, Kentucky 

 coffeetree, redbud, and bladder-senna. It can also be used as an 

 emergency though not a preferred treatment for a number of other 

 species having impermeable seed coats (26). 



Concentrated commercial sulfuric acid with a specific gravity of 

 1.84, undiluted, is recommended for this purpose. Length of treat- 

 ment varies from 20 minutes to 4 hours for the different species, 

 generally with some variation for different seed lots of the same species, 

 depending largely upon age and the degree of drying the seed has 

 undergone. It is a wise precaution to run preliminary tests to deter- 

 mine the minimum treatment to which the particular lot of seed will 

 respond. Efficiency of the treatment is determined by the percent 

 of seed which swell after being rinsed and placed in cold water for 1 

 or 2 days. 



Before treating with acid, the seed should be thoroughly air-dried 

 to avoid injury from excess heat generated when the acid absorbs 

 water. There is less danger of excessive heating if the seed is treated 

 in comparatively small lots. While undergoing treatment, the seed 

 should be stirred frequently. 



Glazed porcelain crocks or wooden tubs are the preferred containers 

 for treating seed in acid. Wooden tubs become charred on the inside 

 and last for some time. Most metal continers are corroded by the acid 

 but if lined with paraffin, asphalt, or lead may be used without diffi- 

 culty. Containers in which treatment is given, or in which acid is 

 stored, should be kept free from extraneous matter, especially other 

 chemicals, and should be plainly labeled. 



Acid may be recovered and, although brown and sirupy, may be 

 used repeatedly, but there will be considerable shrinkage in volume, 

 largely because the acid adheres to the seed and is lost in rinsing. 



After the acid has been used a number of times, it may be advisable 

 to test it with a hydrometer to determine whether there is any marked 

 change in specific gravity. Any appreciable admixture of water in 

 the acid should be avoided. 



A good alternate method is to pour just enough acid over the seed 

 to coat it thoroughly when stirred. Frequent stirring is necessary to 

 obtain uniform treatment. After the seed has been treated for the 



