In the eyes of most aquarists plants have merely a decorative function in the aquarium. Several aquarists, however, have made the plants the subject of their special interest, and it is for these people that Professor De Wit actually wrote his book. In order to make it easier for them he has not followed the usual systematic arrangement of the species but has arranged the species according to their habit. The following growthforms are dealt with successively: 1. Plants freely floating on the surface; 2. Submerged but freely floating plants; 3. Rooting plants with rosettes of filiform, linear, or ribbon-shaped leaves; 4. Plants with leaf-rosettes on the bottom; 5. Rooting plants with floating leaves; 6. Plants with creeping stems and erect leaves; and 7. Plants with erect leaf-bearing stems. There are, however, many species that can be classified in more than one of these vague categories, e.g. Elisma natans, Potamogeton octandrus, many species of Sagittaria and Echinodorus, and all Ceratophyllum species. Two species, Wolffiella floridana and Riccia fluitans, are erroneously classified as plants floating on the surface; they are submerged pleustophytes.