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Horticulture Principles and Practices

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weighed <strong>and</strong> a percentage is derived. Other crop <strong>and</strong> weed seeds are identified so they<br />

can be listed on the lab report. The lab uses a variety of texts <strong>and</strong> seed herbariums to identify<br />

contaminants. Virtual herbariums are becoming popular for seed identification<br />

because of their fast search mechanisms <strong>and</strong> ease of use. http://www.seedimages.com is<br />

a good example of a virtual seed herbarium.<br />

In addition to tweezers <strong>and</strong> magnification, a purity analyst may use an array of<br />

other tools to help separate the components. Screens (to separate seed according to size<br />

<strong>and</strong> shape) (Figures 5 <strong>and</strong> 6) <strong>and</strong> seed blowers (separates according to density) are valuable<br />

tools that speed the process up (Figures 7, <strong>and</strong> 8).<br />

Viability Testing<br />

There are two common types of viability testing: germination <strong>and</strong> tetrazolium (TZ).<br />

Only a h<strong>and</strong>ful of states allow TZ test results to be used for labeling, so the industry relies<br />

heavily on the germination test as the benchmark for viability.<br />

FIGURE 5 Round screens used for small seed can<br />

separate seed based on size <strong>and</strong> shape. (Source:<br />

Annette Miller, USDA-ARS National Center for Genetic Resources<br />

Preservation. Fort Collins, Colorado).<br />

FIGURE 6 Square screens are used to separate<br />

larger seeds based on size <strong>and</strong> shape. (Source: Annette<br />

Miller, USDA-ARS National Center for Genetic Resources Preservation.<br />

Fort Collins, Colorado).<br />

FIGURE 7 A seed blower<br />

separates based on density, <strong>and</strong><br />

is used for removing chaff,<br />

empty seeds, or other contaminants.<br />

(Source: Annette Miller, USDA-<br />

ARS National Center for Genetic<br />

Resources Preservation. Fort Collins, Colorado).<br />

FIGURE 8 Magnifying lamps make it easier to see<br />

weeds. (Source: Annette Miller, USDA-ARS National Center for<br />

Genetic Resources Preservation. Fort Collins, Colorado).<br />

290 Chapter 9 Sexual Propagation

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