THE PAST HISTORY OF PLANTS. 207 



plants may be briefly described in rough outline. 

 First of all we get the simple one-celled plant, the 

 lowest type of all, consisting of a single mass 

 of protoplasm, generally with chlorophyll, sur- 

 rounded by a cell-wall. Next above these come 

 the hair-like water-weeds, which consist of rows of 

 such simple cells, placed end to end in single file, 

 one in front of another, like pearls in a necklace. 

 These kinds are many-celled, but each cell is here 

 in contact with two others only, one below, and 

 one above it. Thirdly, we get the flat leaf-like 

 water-weeds, which have thin green fronds, com- 

 posed 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 ordinary 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 vas- 

 cular plants with stems, leaves, and branches. 



Most of these cellular plants, when they pos- 

 sess 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 dis- 

 tinction, however, is not a genealogical one. Cel- 

 lular 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 m their absence of green 

 colour, in their usual whiteness and fleshiness, and 

 in their mushroom-like substance, they do not 

 really form a natural class ; their resemblance is 



