INTERPRETING GERMINATION RESULTS BASED ON DIFFERING EMBRYONIC EMERGENCE CRITERIA

Weed germination studies often quantify only radicle emergence to indi cate germinated seeds. Four categories were used to investigate root a nd shoot emergence from germinating seeds including: root (seeds with radicles emerged); shoot (seeds with plumules or cotyledons emerged); complete (both roots and plumules emerged); and total (any emergence: roots, shoots, or both). Medusahead and yellow starthistle germination tests illustrated that emergence was equal in the root and total cate gories. Shoot and complete categories had identical counts, but those counts were often different from the total and root categories. Emerge nce of medusahead shoots at 8 C was 3 d later than roots, but at 18 C roots and shoots emerged nearly simultaneously. Yellow starthistle roo ts were not affected by picloram, but emergence of cotyledons (shoot c ategory) was reduced by 80%. Yellow starthistle seeds stored for 74 an d 90 mo produced more radicles than cotyledons after 28 d at 28 C. Med usahead and yellow starthistle root emergence in the laboratory someti mes exceeded seedling emergence from a greenhouse soil mixture. The pr esence of both roots and shoots (complete category) was the most accur ate criterion for documenting yellow starthistle and medusahead seed r esponse to laboratory test conditions.