1. (1) Unit of certification. A portion of a field may be certified if the area to be certified is clearly defined. Portions of a field not meeting requirements for certification must not be allowed to reach the seed stage.

2. (2) Isolation. A field producing foundation, registered or certified seed must have the minimum isolation distance from fields of any other variety or fields of the same variety that do not meet the varietal purity requirements for certification, as given in the following table:

   Class	Fields of less than five acres	Fields of five acres or more
   Foundation	80 rods	80 rods
   Registered	40 rods	20 rods
   Certified	20 rods	10 rods
   Between different seed classes of same variety except the certified class of nonhardy southwest varieties	10 rods	10 rods

3. (3) Volunteer plants. Volunteer plants shall be cause for rejection or reclassification of a seed field.

4. (4) Seed fields outside region of adaptation. Certification of seed fields outside regions of adaptation of a variety shall be limited to stands not exceeding six years of age.

   (b) Specific requirements.

   Maximum permitted in each class
   Factor	Foundation	Registered	Certified
   Other varieties 1	0.2%	0.5%	1.0%
   Sweet clover	none	10 plants per acre	160 plants per acre

   1

   Other varieties shall be considered to include offtype plants and plants that can be differentiated from the variety that is being inspected.

(a) General.