The quantitative model developed predicts the allocation of energy in plants to sexual and vegetative reproduction by analyzing relative costs and benefits. The model incorporates the cost of nutrients. The concepts of environmental information and uncertainty are used to assess the plant's estimate of reproductive success. The model specifically predicts changes in reproductive effort in response to changes in nutrients, shade, crowding, and environmental cues. The model is compared with r versus K theory, allometric, demographic, and other models. It is shown that the models are experimentally distinguishable and that the data do tend to support the benefit-cost model.