Permanent preservation of these algae is most adequately assured by drying. The dried specimens can be placed in paper packets, labeled, and stored in the herbarium. Since most of the species thrive best in subaerial or temporarily inundated habitats, they exist for much of the year in the dried condition in nature. Wet algae can be laid top-side up on paper and allowed to dry in the open air. Drying in a plant press excludes the air, so that autolyzation of the protoplasm takes place; drying with heat often destroys the cells by cooking. If possible, part of the substratum should be preserved as part of the specimen. If the plants are microscopic and mixed with other algae, a good specimen should contain a sufficient number of the plants so that at least several may be found in every field of every mount made for microscopic study.