now PLANTS OBTAIN WATER. 23 



cases absorption takes place throu£;h all portions of the surface in contact 

 with the water, as in spirogvra, vaucheria, and all of the larger seaweeds. 

 Comparatively few of the alga; grow on the surfat es of rocks or trees. It 

 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 algae are parasitic, Ii\'ing 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 im- 

 mersed in water. In other forms, like mucor, a portion of the mycelium 

 is within the substratum, and being bathed by the water or watery solu- 

 tions 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. 



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 know 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 dichot- 

 omous manner, the character- 

 i.'tic 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 w'hich resemble root 

 hairs and serve the same pur- 

 pose in the processes of absorp- 

 tion. Another species of riccia Fir 

 (R. crv-stallina) is shown in fig. Thalljs ct Riccia lutescens. 

 252. This plant is quite circular in outhne and occtirs on muddy flats. 

 Some species float on the water. 



47. Marcliantia. — One of the larger and coarser liverworts is 

 figured at 31. This is a very common liverwort, growing in 

 very damp and muddy places and also along the margins of 

 streams, on the mud or upon the surfaces of rocks which are 



