DIFFERENCES BETWEEN ANIMALS AND PLANTS 221 



but when we come to consider low types, some or all of these 

 distinctions disappear. There are, for example, many plants 

 which have no chlorophyll (molds, toadstools, etc.), and hence 

 have no power of photosynthesis; but they are, nevertheless, 

 clearly plants, for no one would for an instant think of con- 

 fusing them with animals, even though they do not contain 

 chlorophyll. Some plants have independent motion, while 

 some animals are stationary. Some plants are sensitive. The 

 distinction of shape applies only to the higher organisms; for 

 among the microscopic forms no distinction can be seen be- 

 tween the shape of animals and plants, some animals having 

 no mouth, and some plants, as well as animals, having their 

 bodies condensed rather than expanded. Thus it appears 

 that each of the distinguishing characters separating animals 

 and plants breaks down when we come to apply it closely to 

 some of the low forms of life ; until we have to admit that there 

 is no absolute criterion separating the two kingdoms. 



Nevertheless, there is rarely any real difficulty in making 

 the distinction. It is true that there is a difference of opinion 

 as to whether a few of the very low forms should be called 

 animals or plants; but when we take all of the above facts into 

 consideration, it is only in a few instances that we are unable 

 to say positively that any given organism is either animal or 

 plant. Most of the difficulty is confined to the microscopic 

 forms which are among the lowest organisms, and the fact that 

 among these there is no absolutely fixed line between the two 

 kingdoms is of special significance as suggesting the origin of 

 the two kingdoms from a common starting point by a process 

 of evolution. 



Organisms which possess chlorophyll, and consequently nour- 

 ish themselves by photosynthesis, are sometimes said to be holo- 

 phytic (Gr. holos = whole + phyton = plant) . In contradistinc- 

 tion, organisms which have no chlorophyll and must depend 

 upon others for sustenance are called holozoic (Gr. zoon = ani- 

 mal). Animals are practically all holozoic, and green plants 



