(a) The working sample shall be weighed in grams to four significant figures and shall then be separated into four parts: (1) Kind or variety to be considered pure seed, (2) other crop seed, (3) weed seed, and (4) inert matter. The components shall be weighed in grams to the same number of decimal places as the working sample. The percentage of each part shall be determined to two decimal places.
(b) Aids for the classification of pure seed, other crop seed, weed seed, and inert matter may include visual examination, use of transmitted light (diaphanoscope), or specific gravity (seed blowers). Specific instructions for classification of the various components are given in Secs. 201.47a to 201.51, inclusive.
(c) The components shall be weighed and percentages calculated as follows:
(1) For sample sizes less than 25 grams, all four components shall be weighed; the percentages shall be based on the sum of these weights and not on the original weight. The sum of these weights shall be compared with the original weight of the working sample as a check against the loss of material, or other errors.
(2) For sample sizes of 25 grams or more, the components--other crop seed, weed seed, and inert matter--shall be weighed separately and their percentages determined by dividing these weights by the original weight of the working sample. The pure seed need not be weighed; its percentage may be determined by subtracting the sum of the percentages of the other three components from 100.
(3) When rounding off the calculated percentages of each component to the second decimal place, round down if the third decimal place is 4 or less and round up if the third decimal place is 5 or more, except that if any component is determined to be present in any amount calculated to be less than 0.015 percent, then that component shall be reported as 0.01 percent. If any component is not found in the purity analysis, then that component shall be reported as 0.00 percent.
(4) The total percentage of all components shall be 100.00 percent. If the total does not equal 100.00 percent (e.g. 99.99 percent or 100.01 percent), then add to or subtract from the component with the largest value (usually the pure seed component).
(d) When the working sample consists of two or more similar kinds or varieties which would be difficult to separate in the entire sample, it is permissible to weigh the similar kinds or varieties together as one component and make the separation on a reduced portion of the sample. At least 400 seeds or an equivalent weight shall be taken indiscriminately from the pure seed component and the separation made on this portion. The proportion of each kind present shall then be determined by weight and from this the percentage in the entire sample shall be calculated.
(e) The Uniform Blowing Procedure described in Sec. 201.51a(a) shall be used for the separation of pure seed and inert matter in seeds of Kentucky bluegrass, Canada bluegrass, rough bluegrass, Pensacola variety of bahiagrass, orchardgrass, side-oats grama, and blue grama.
(f) Procedures for purity analysis for coated seed are given in Sec. 201.51b. [25 FR 8770, Sept. 13, 1960, as amended at 30 FR 7890, June 18, 1965; 46 FR 53635, Oct. 29, 1981; 59 FR 64497, Dec. 14, 1994; 65 FR 1707, Jan. 11, 2000] Sec. 201.47a Seed unit.
The seed unit is the structure usually regarded as a seed in planting practices and in commercial channels. The seed unit may consist of one or more of the following structures:
(a) True seeds;
(b) For the grass family:
(1) Caryopses and single florets;
(2) Multiple florets and spikelets in tall oatgrass (Arrhenatherum elatius), oat (Avena spp.), gramas (Bouteloua spp.), rhodesgrass (Chloris gayana), barley (Hordeum vulgare), and bluegrass (Poa spp.);
(3) Entire spikelets in bahiagrass, bentgrasses, dallisgrass, guineagrass, browntop millet, foxtail millet, proso millet, panicgrasses, redtop, rice, switchgrass, and vaseygrass. Entire spikelets which may have attached rachis segments, pedicels, and sterile spikelets in big bluestem, little bluestem, sand bluestem, yellow bluestem, bottlebrush-squirreltail, broomcorn, yellow indiangrass, johnsongrass, sorghum, sorghum- sudangrass, sorghum almum, sorgrass, and sudangrass;
(4) Spikelet groups:
(i) Spikelet groups that disarticulate as a unit in galletagrass;
(ii) Spikelet groups that disarticulate as units with attached rachis and internodes in bluestems, side-oats grama, and yellow indiangrass;
(5) Fascicles of buffelgrass (Cenchrus ciliaris) consisting of bristles and spikelets;
(6) Burs of buffalograss (Buchloe dactyloides);
(7) Bulblets of bulbous bluegrass (Poa bulbosa);
(8) Multiple units as defined in Sec. 201.51a(b)(1).
(c) Dry indehiscent fruits in the following plant families: Buckwheat (Polygonaceae), sunflower (Compositae), geranium (Geraniaceae), goosefoot (Chenopodiaceae), and valerian (Valerianaceae);
(d) One- and two-seeded pods of small-seeded legumes (Leguminosae), burs of the burclovers (Medicago arabica, M. polymorpha), and pods of peanuts (Arachis hypogaea). (This does not preclude the shelling of small-seeded legumes for purposes of identification.) Pods of legumes normally containing more than two seeds, when occurring incidentally in the working sample, should be hulled if the kind is hulled when marketed;
(e) Fruits or half fruits in the carrot family (Umbelliferae);
(f) Nutlets in the following plant families: Borage (Boraginaceae), mint (Labiatae), and vervain (Verbenaceae);
(g) ``Seed balls'' or portions thereof in multigerm beets, and fruits with accessory structures such as occur in other Chenopodiaceae and New Zealand spinach. For forage kochia refer to Sec. 201.48(j) and Sec. 201.51(a)(7). [46 FR 53636, Oct. 29, 1981, as amended at 59 FR 64497, Dec. 14, 1994; 65 FR 1707, Jan. 11, 2000] Sec. 201.47b Working samples.
The purity working sample is the sample on which the purity analysis is made. The noxious-weed seed working sample is the sample on which the noxious-weed seed examination is made. [20 FR 7930, Oct. 21, 1955]