226 THE STOKY OF THE PLANTS. 



weeds, which have thin green fronds, composed 

 of a single broad sheet of cells, not a hair-like 

 row ; each cell has here many cells around it, 

 but all lie in one plane ; the sheet is only one 

 cell thick ; it does not spread abroad in more 

 than two directions. Lastly, we get the ordi- 

 nary thick-fronded seaweed, in which sheets of 

 cells, many layers deep, grow in divided masses 

 on rope-like bases, and closely resemble to the 

 eye true vascular plants with stems, leaves, and 

 branches. 



Most of these cellular plants, when they 

 possess green chlorophyll, are known as algce. 



There are several low forms of plants, how- 

 ever, which do not possess chlorophyll, but live 

 at the expense of other plants, exactly as 

 animals do. These are generally known in the 

 lump as fungi. Many of them are terrestrial. 

 The distinction, however, is not a genealogical 

 one. Cellular plants of various grades have 

 often taken, time after time, to this lower 

 parasitic or carrion-eating habit ; and though 

 they therefore resemble one another externally 

 in their absence of green colour, in their usual 

 whiteness and fleshiness, and in their mush- 

 room-like substance, they do not really form a 

 natural class ; their resemblance is due to their 

 habits only. In short, we call any cellular plant 

 a fungus, if instead of supporting itself by green 

 cells, it has adopted the trick of living on 

 organised material already laid up by other 

 plants or animals. 



Among these fungus-like plants, again, some 

 of the simplest and lowest are the celebrated 



