CREATION BY EVOLUTION 



aquatic plants, became readapted to an aquatic existence. 

 One group after another thus became dominant and then 

 waned or became entirely extinct. The accompanying dia- 

 gram (Fig. 1) illustrates the successive numerical dominance 

 of different plant types and the increasing complexity of 

 the vegetable kingdom as a whole. 



Another principle is illustrated by the progressive loss of 

 plasticity in organisms or organs as they became more com- 

 plex and more highly specialized. The simpler organisms 

 outlasted the complex or gave origin to new types, for the 

 more complex lost adaptability to new conditions and per- 

 ished during changes of environment. Most of the earlier 

 forms of the successive groups of plants were synthetic or 

 generalized in structure. The earliest ferns, for example, 

 show combinations of features that subsequently became the 

 property of different fern families, and the seed ferns com- 

 bined the features of ferns and cycads. 



The first simple plants, which grew in the water, prob- 

 ably lacked the substance commonly called leaf green 

 (chlorophyll) ; they obtained their nitrogen from ammonia 

 compounds and gained their energy by oxidation, in much 

 the same way that some modern bacteria oxidize iron and 

 sulphur. With the development of chlorophyll they were 

 able to utilize directly the carbon dioxide of the air and build 

 up complex organic compounds. The acquisition of this 

 power of using inorganic material for food and of convert- 

 ing sunshine into energy marks the first progressive step in 

 the history of plants. The second step was the occupation 

 of the land. During the long history of land floras, covering 

 millions of years, the two principal advances were the devel- 

 opment of what is called secondary wood, such as forms the 

 seasonal layers of the oaks or the pines, which enables them 



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