THE WONDERS OF LIFE 



cannot support life without the addition of organic 

 compounds; but we| can make them grow in a food 

 solution consisting of sugar and purely inorganic nitrog- 

 enous salts. Thus they are on the border that separates 

 the plasmodomous plants from the plasmophagous 

 animals. Like the latter, the fungi have evolved from 

 the plants through changed food conditions. We find 

 this process even among the unicellular protists in the 

 phycomycetes, which descend from the siphonea. In 

 the same way the real multicellular fungi (ascomycetes 

 and basimycetes) may be traced to the tissue-forming 

 algie. 



All true animals have to derive their food from the 

 plant kingdom, the vegetal feeders directly, and the flesh 

 feeders indirectly, when they consume vegetal feeders. 

 Hence the animals are, in a certain sense, as the older 

 natural philosophy put it four hundred years ago, 

 "parasites of the plant world." From the point of view 

 of phylogeny, the animal kingdom is, therefore, clearly 

 much younger than the plant kingdom. The develop- 

 ment of the animals from the plants was determined 

 originally by a change in the method of nutrition which 

 we call metasitism. 



The chemical modification of the living matter which 

 is connected with the loss of plasmodomism — in other 

 words, the conversion of the reducing phytoplasm into 

 oxidizing zooplasm — must be regarded as one of the 

 most important changes in the history of organic life. 

 This "reversal of metabolism" is polyphyletic ; it has 

 been repeated many times in the course of biological 

 history, and has taken place independently in very 

 different groups of the organic world — whenever a 

 plasmodomous cell or group of cells ( = tissue) had 

 occasion to feed directly on ready-made plasm, instead 

 of giving itself the trouble of building it up out of 

 inorganic compounds. We see this particularly among 



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