The Simplest Plants 8i 



lump withdraws from the point of disturbance, or it rounds 

 up into a nearly spherical mass. Chemical changes of vari- 

 ous kinds go on internally, some continuously and others in 

 response to changed conditions. 



The ameba is typical, in its way of life, of thousands 

 of animal species in which the individual's body is not sub- 

 divided into " cells." Some of these live in fresh water, some 

 in i>alt water. Some are parasitic in the intestines or blood 

 or other parts of higher animals; and some are parasitic upon 

 plants. In some groups of these so-called one-celled animals 

 the protoplasm or living substance protrudes as fine vibrat- 



FlG. 17. DiFFLUGIA 



This microscopic animal is representative of a large group 

 in which the individual is like an ameba that builds a shell 

 out of tiny sand particles. 



ing threads or lashes, by means of which the animal moves 

 through the water. In some species a delicate armor is con- 

 structed of sand particles (Fig. 17). In some species repro- 

 duction takes place by a true sexual process, whereby two 

 special structures (or entire individuals) unite as in fertiliza- 

 tion to give rise to a new individual. In some species there 

 are formed special non- sexual reproductive cells or spores. 

 The parasite which is the cause of malaria is a relative of 

 ameba that reproduces by both methods. 



The Stumpiest 'Plants 



Among the plants as well as among the animals the 

 simplest forms consist of individuals that are not made up 



