The relationship between language, thought, and concept formation has been a central issue in many studies and theoretical discussions in various domains--philosophy, psychology, anthropology, and linguistics. The relation between language and concept development can be framed as two opposing questions: (1) Does the child learn concepts first and then later attach words to them? or (2) Are concepts formed when a child tries to attach meanings to words she hears? The purpose of this study was to investigate the relationship between language and the development of children's conception of plants as living things. This was done by comparing the responses of children with different mother tongues (Hebrew and English) to different tasks (verbal and non-verbal) related to the conception of plants as living things. The children (N=696) were from each of grades 2, 3, 4, 5, and 6 in Canada and Israel. It was found that both groups of children were less successful in the non-verbal task than in the verbal task, and that Hebrew-speaking children performed at a lower level than English-speaking children in both the verbal and non-verbal tasks. These findings suggest that the difficulty in classifying plants as living things is conceptual in origin and may also suggest that language affects concept development on both the verbal and perceptual levels. (KM)