Indicator papers from plant extracts

To determine the allelopathic potential of campestris and oleracea var. italica, leachates from each species were made. Extracts were prepared by soaking, for two hr, weighed amounts of fresh or dried material in sufficient doubly distilled water to prepare a 10% extract (of fresh material) or 1.5% extract (of dry material). Extracts were vacuum filtered through paper (Whatman 1). The osmotic concentration was measured with a freezing-point osmometer (0 to 500 mosm) and indicator seeds were soaked in 10 mL of the extract for an hour prior to planting. 

Radicle elongation was a more sensitive measure than germination. Phytotoxicity decreased as the distance from rye shoot material to assay seeds increased. Generally, cress and lettuce were more sensitive indicators than the grass species tested. Phytotoxic compounds from shoots were water extractable. To evaluate the effect of plant part and quantity of residue, roots, shoots, or both were assayed at 0.0, 0.25, 0.5, 1.0, and 2.0 g/dish and placed 5 mm away from the assay seed. Similar amounts of paper towels were used as controls. Shoot tissue was about twice as toxic as root tissue. The data suggested that under field conditions, a... 

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