Leaf litter of 239 medicinal plant species were collected from the Izu Experimental Station for Medicinal Plants, National Institute of Health Sciences, Shizuoka, Japan, and these were subjected to analysis of their allelopathic effects using the sandwich method, as shown in Figure 1. We used lettuce (Lactuca sativa L. Great Lakes 366, Takii Seed Co. Ltd, Japan) as a test plant material in the bioassay because of its reliability for germination, easiness of purchase, and susceptibility to inhibitory and stimulatory chemicals (Fujii et al. 1990).
image Figure 1. Sandwich method: (a) six-well multidish plastic plate; (b) 10 or