Explains the mechanisms and describes the processes that underlie gravitropism in roots. Reviews experimental efforts and investigative results that explored the causes of root behavior. (ML)

Historically described are research studies which led to the current explanation of the two kinds of intracellular transport-axoplasmic flow and axoral transport. Models explaining their fundamental mechanism and the kinds of materials they convey are presented. (BT)

Described are animals that can filter their food out of the water. Various structures modified to strain plankton and small animals from water are detailed. The adaptive significance of these structures is discussed. (CW)

Describes the decline in people's ability to focus their eyes as their age increases. Discusses probable causes of this effect including changes in the eye's geometry and biochemistry. Diagrammatically illustrates age related changes in the lens of the human eye. (CW)

Investigates memory storage and molecular nature of associative-memory formation by analyzing Pavlovian conditioning in marine snails and rabbits. Presented is the design of a computer-based memory system (neural networks) using the rules acquired in the investigation. Reports that the artificial network recognized patterns well. (YP)