Cnapter 1 



TWO PATTERNS OF UFE 



It is a familiar fact that the living world which surrounds us 

 and of which we are an integral part consists of two kinds of 

 organisms, each of which has developed a pattern of living suc- 

 cessful in its own way. One is represented by the animal king- 

 dom which, since it displays so many characteristics similar to 

 our own, we are likely to think of as being more or less typical of 

 all life. But the three quarters of a million species which constitute 

 the animal kingdom are the end-product of an experiment with 

 only one pattern of existence; we can not appreciate fully the 

 potentialities and importance of living things by limiting our 

 knowledge of life to the animal kingdom. The other pattern of 

 living has been developed by plants, with a resulting diversity 

 of a quarter of a million species. The more familiar members 

 of both kingdoms have attained a degree of complexity which 

 obscures fundamental similarities, giving the casual observer the 

 impression that a wide gulf exists between a plant and an animal. 

 It is hard to believe, at first sight, that seaweeds have much in 

 common with the fish swimming among them, or deer with the 

 grass upon which they are grazing. But to the biologist these two 

 patterns of life show many similarities indicating a common 

 origin in the geologic past. Before we attempt to define a plant, 

 or to isolate the basic diff'erences which underlie the two king- 

 doms, it might be well to consider a few of the more important 

 traits that plants and animals have in common. 



Protoplasm 



Life as we know it is always found in conjunction with a 

 physical basis of protoplasm, the tangible substance out of which 

 all living things are made. Plant and animal protoplasm are 

 essentially alike in appearance and composition — there is little 



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