Biology. Highly resistant dehydrated form of reproductive cells of algae, fungi, and nonflowering plants. They have a low metabolic rate and very resistant cell walls against dehydration. Thus they can survive a long time of unfavorable environmental conditions. Compared to bacterial spores they are not heat resistent.
2. Microbiology. Highly resistant, especially against heat, form of bacteria (e.g., species of bacillus and clostridium).