CHAPTER IX 



PLANTS AND ANIMALS 



Two great groups of living things exist, plants and animals. The 

 higher forms of the two are readily recognized, but the simpler ones lack 

 the characteristics which serve to distinguish the higher types. Many 

 simple living things cannot be satisfactorily assigned to either category. 

 A German named Haeckel suggested as a way out of this difficulty that 

 an intermediate group, which he termed Protista, be recognized. This sug- 

 gestion, however, has not beenfollowed, because it would simply double the 

 difficulty — instead of having to draw one line of demarcation which is very 

 uncertain, it would be necessary to draw two lines, both as uncertain. 



66. Comparison between Plants and Animals. — In many respects 

 plants and animals agree. The protoplasm of which both are composed 

 is, as far as can be seen, essentially the same. Although plant and animal 

 cells have certain features which aid in their discrimination, those fea- 

 tures are not essential characteristics of the protoplasm of which they 

 are composed, and as far as present knowledge goes, the protoplasm of 

 the two is indistinguishable. Indeed, it is generally assumed that there 

 was but one creation of life on this earth and that from that first created 

 life both plants and animals have sprung. This makes quite intelligible 

 the difficulty in distinguishing between the simpler forms of the two. 

 Metabolism is carried on essentially in the same manner in plants as in 

 animals. Plants and animals have many activities in common and 

 those in which they differ are developed gradually in passing from lower 

 to higher forms. The lower plants are termed protophytes and the 

 higher metaphytes, while the lower animals are called protozoans and 

 the higher metazoans. The unit of plant structure is the cell, as is also 

 the unit of animal structure, and plant cells present the same phenomena 

 in connection with their multiplication as do animal cells. They are 

 affected in a similar manner by various external forces. The higher 

 forms of both possess sex. The mechanism of inheritance is the same and 

 the phenomena connected with inheritance are also quite comparable in 

 plants and animals. 



67. Biology. — Because of the fact that there are many things in 

 common between plants and animals, the subjects of botany and zoology 

 are frequently considered as parts of one larger subject termed biology. 

 It has to do with all that concerns living things in general and may be 

 conceived of as divided into the two fields botany and zoology. In the 

 further division of these two fields each can be divided into a series of 



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