In nearly all of the algæ the plant body is submerged in water. In these cases absorption takes place through all portions of the surface in contact with the water, as in spirogyra, vaucheria, and all of the larger seaweeds. Comparatively few of the algæ grow on the surfaces of rocks or trees. In these examples it is likely that at times only portions of the plant body serve in the process of absorption of water from the substratum. A few of the algæ are parasitic, living in the tissues of higher plants, where they are surrounded by the water or liquids within the host. Absorption takes place in the same way in many of the fungi. The aquatic fungi are immersed in water. In other forms, like mucor, a portion of the mycelium is within the substratum, and being bathed by the water or watery solutions absorbs the same, while the fruiting portion and the aerial mycelium obtain their water and food solutions from the mycelium in the substratum. In higher fungi, like the mushrooms, the mycelium within the ground or decaying wood absorbs the water necessary for the fruiting portion; while in the case of the parasitic fungi the mycelium lies in the water or liquid within the host. [Illustration: Fig. 30. Thallus of Riccia lutescens.] =46. Absorption by liverworts.=—In many of the plants termed liverworts the vegetative part of the plant is a thin, flattened, more or less elongated green body known as a thallus. _Riccia._—One of these, belonging to the genus riccia, is shown in fig. 30. Its shape is somewhat like that of a minute ribbon which is forked at intervals in a dichotomous manner, the characteristic kind of branching found in these thalloid liverworts. This riccia (known as R. lutescens) occurs on damp soil; long, slender, hair-like processes grow out from the under surface of the thallus which resemble root hairs and serve the same purpose in the processes of absorption. Another species of riccia (R. crystallina) is shown in fig. 252. This plant is quite circular in outline and occurs on muddy flats. Some species float on the water.