DEVELOPMENT AND FUNCTIONS OP CELLS. 41 



their beauties. The same distinction of parts into root, stem, 

 and leaves is therefore still seen in these minute, but exquisite- 

 ly beautiful plants, although the root no longer springs from 

 one extremity of the axis of growth, but from every part of it. 



45. In the Liverworts, the leaves are reduced to mere im- 

 bricated scales, and in the lower forms "become blended into 

 a continuous expansion of vegetable matter called a frond. 



46. In the Lichens, vegetation is reduced to its last degree 

 of simplicity. Root, stem, and leaves have now disappeared, 

 and the whole plant is blended into a flat expansion or bed of 

 vegetable matter, called a thallus. The thalli of the higher 

 forms of lichens are foliaceous, consisting of several layers of 

 cells radiating out on all sides ; some of these cells are repro- 

 ductive, and exhibit the spores in the shape of powdery heaps 

 called soredia, or else they become organized into saucer-like 

 bodies called shields, in which the spores are imbedded. In 

 the lower forms, the thalli of these plants are crustaceous or 

 even pulverulent, the whole plant assuming the appearance of 

 mere powder. In this case the cells no longer remain together, 

 but are free and unformed, any cell being capable of originat- 

 ing a new individual. The plant and cell are now identical. 



47. Nature passes through the same transitions in the Sea- 

 weed tribe. Certain Algse or sea-weed are of- a frondose, 

 others of a filamentous structure, whilst some appear as mere 

 scum on the surface of the waves. In these instances, the 

 plants consist of cells developing in length and breadth, of 

 cells developing in length only, or of a single cell. The same 

 remark applies to the Fungi, whore nature only finishes with 



