INTRODUCTORY 



5 



the simplest forms of life whose structure is largely confined within 

 the limits of a single cell, asexual reproduction or multiplication 

 by division is the common rule, while the idea of sex was more 

 fully developed among slightly higher forms as the result of new 

 and distinctly higher necessities in the struggle for life. 



The distinctions between the simple forms of green plants and 

 animals are physiological rather than structural, since both are 

 simple masses of protoplasm, enveloped or not in a cell wall as 

 the case may be. But the possession of chlorophyl by the green 

 plant renders it a peculiar organism with the ability to utilize the 

 strictly inorganic components of air, water and mineral salts, and 

 through the energy of sunlight manufacture them into complex 

 organic compounds. The chemical function of green plants is 

 thus synthetic, producing complex molecules from much more 

 simple ones. 



Animals, on the contrary, depend for their life on organic food, 

 first manufactured by the green plants. This simple difference 

 of function in the simple one -celled organisms has resulted in the 

 important distinctions that rapidly appeared as the one-celled 

 organisms increased in complexity and became the higher animals 

 and higher plants. In the struggle for food, while the plants 

 found their supply in the air and water in which they were bathed, 

 the animals were forced to seek their supply and hence arose the 

 principle of locomotion and with this as complexity of structure 

 increased, there came the necessity for an elaborate but compact 

 digestive, circulatory and respiratory system ; with locomotion 

 also came the necessity in the struggle for life to seek safety and 

 avoid danger, hence the elaborate system of special senses that 

 are the peculiar endowment of all the higher animals. 



On the other hand, since the plant had no necessity to seek its 

 food, it had no need for locomotion, and except in the case of a 

 few special organs it has never developed the power. Being sta- 

 tionary, compactness cut no figure in its needs, and in proportion 

 as its size increased, it spread itself out in root and leaf to offer as 

 wide an absorptive surface as possible to the media from which it 

 draws its sustenance. Being stationary it has had no need of 

 sight or hearing or the other special senses of animals, because it 

 could neither avoid danger nor retreat to a place of safety had 

 they been developed. On the contrary, it has developed special 



