CHAPTER XII. 



NUTRITION AND MEMBERS OF THE PLANT BODY. 



166. In connection with the study of the means for obtaining nutriment 

 from the soil or water by the green plants it will be found convenient to 

 observe carefully the various forms of the plant. Without going into detail 

 here the suggestion is made that simple thread forms like spirogyra, cedogo- 

 nium, and vaucheria ; expanded masses of cells as are found in the thalloid 

 liverworts, the duckweed, etc. , be compared with those liverworts, and with the 

 mosses, where leaf-like expansions of a central axis have been differentiated, 

 and how this differentiation, from the physiological standpoint, has been 

 carried farther in the higher land plants. 



167- Nutrition of 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. 

 58. Its shape is somewhat like that of a minute ribbon which is forked at 



intervals in a dichotomous man- 

 ner, the characteristic kind of 

 branching found in these thalloid 

 liverworts. This riccia (known 

 as R. lutescens) occurs on damp 

 soil; long, slender, hair-like 

 1 processes grow out from the 

 under surface of the thallus, 

 which resemble root hairs and 

 serve the same purpose in the 

 processes of nutrition. Another 

 species of riccia (R. crystallina) 

 is shown in fig. 171. This plant 

 is quite circular in outline and 

 occurs on muddy flats. Some 

 species float on the water. 



168. Marchantia. — One of the larger and coarser liverworts 

 is figured at 59. This is a very common liverwort, growing in 



70 



Fig. 58. 

 Thallus of riccia lutescens. 



