Plant genetic resources. II. The Author describes the actions to be undertaken for the conservation of the plant genetic resources, mainly in relation to the following methods: a) natural mass reservoirs where plant material may continue its processes of evolution, b) collections managed in such way that the genetic integrity of the original population is not eroded. Criteria, methodologies, studies, problems solved or to be solved are considered in the paper. Great attention is deserved to tactics of exploration and collection, to storage conditions, to seed physiology and life span of seeds, to information storage and documentation.