THE PLANT AND ANIMAL COMPARED. 167 



ferences between the plant and animal is fundamentally important 

 save the mode of nutrition. The worm must have complex food 

 including proteid matter. The fern is able to manufacture this 

 complex food out of simple compounds. In terms of energy, 

 the worm requires food rich in potential energy ; the fern can 

 manufacture food from matters poor in energy, building them 

 tip by a chemical synthesis into substances energized by the sun's 

 rays. 



Hence it appears, broadly speaking, that the fern is construc- 

 tive, and stores up energy ; the earthworm is destructive, and 

 dissipates energy. And this becomes of immense importance in 

 view of the fact that the fern is typical in this respect of all green 

 plants, as the earthworm is typical of all animals. 



It will hereafter appear that even this difference, great as it 

 is, is partly bridged over by colorless plants like yeast, moulds, 

 bacteria, etc., which have no chlorophyll, are therefore unable to 

 use the energy of light, and hence must have complex energized 

 food. But these organisms do not, like animals, require proteid 

 matter, being able to extract all needful energy from the simpler 

 fats, carbohydrates, and salts. When we consider that the dis- 

 tinctive peculiarities of animals can thus be reduced to the sole 

 characteristic of dependence on proteid food, we cannot doubt 

 that the differences between plants \are of immeasurably less 

 importance than their fundamental likeness. While the sub- 

 division of biology into botany and zoology is indispensable for 

 the purposes of practical study, it is, after all, adopted mainly for 

 the sake of convenience, and is not marked by any great natural 

 boundary among living things. 



It has been the object of the foregoing chapters to give the 

 student a general conception of organisms, whether vegetal or 

 animal ; of their structure, growth, and mode of action ; of their 

 position in the world of matter and energy, and of their relations 

 to lifeless things. With this preliminary knowledge as a basis, 

 the student is prepared to take up the progressive study of other 

 organisms, selected as convenient types or examples to illustrate 

 the more important outlines of General Biology. It is conveni- 

 ent to begin with low and simple forms and work thence gradu- 

 ally upwards ; and it is further desirable to do so because there 

 is reason to believe that this course corresponds with the path of 



