276 PART IV. — VEGETABLE TAXONOMY. 



CHAPTER IV.— THE THALLOPHYTA (Continued). 



Class II. — The Schizophyta, or Fission Plants. 



These are also very low forms of plant-life, being exceedingly 

 simple in structure, and always minute, some of them being the 

 smallest of known organisms. They are mostly unicellular, or if 

 consisting of cell-aggregates, as is sometimes the case, the cells are 

 united in a simple way, and have very little dependence upon each 

 other. Some possess chlorophyll along with blue coloring matter, 

 and assimilate inorganic food-materials, but many are destitute 

 of chlorophyll, and are either saprophytic or parasitic. 



The chlorophyll forms are usually of larger size and better 

 developed than the chlorophylless ones. A few of the former 

 show a slight differentiation of cells, and rarely some of them 

 produce motile or swarm-spores ; none, however, of the entire 

 class are known to reproduce sexually, the mode of increase in all 

 of them being mainly by fission, though some also multiply by 

 some other form of cell-division. Most of them are endowed 

 with the power of locomotion, and this may be by means of cilia, 

 or it may be produced by bending from side to side when the 

 cells are united in chains ; or, lastly, the cells may be arranged 

 in the form of a spiral, which combines with a progressive mo- 

 tion one of rotation upon its axis, like the motion of a screw 

 when driven into a board. 



The class is divided into two sub-classes : 



The Schizomycetes and the Cyanophycece. 



THE SCHIZOMYCETES. 



The term is compounded of two Greek Words, meaning liter- 

 ally " fission-fungi," in allusion to the way these plants increase, 

 by fission, and to their fungus-like habits. They are commonly 

 known as Bacteria, and are at once the most abundant and the 

 most minute of organisms. The largest of them are not more 

 than the one ten-thousandth of an inch in diameter, and the 

 smallest not more than one-tenth that size. It requires for their 

 study, therefore, the highest and best powers of the microscope. 



