This environmental unit is one of a series designed for integration within an existing curriculum. The unit is self-contained and requires minimal teacher preparation. The philosophy of this series is based on an experience-oriented process that encourages self-paced independent student work. The purpose of this particular unit is to prove that variation does exist within populations. Skills employed in the unit's activities include collection techniques, quantitative measurement methods, record-keeping, and the use of graphs. Materials for study can be collected at a preliminary field trip or from classroom potted plants. Activities are geared for students in grades 4-8. Teacher information such as materials, background information, and additional, more sophisticated topics is given. (MA)