46 evolution: the ages and tomorrow 



earnestly awake may gain understanding. In spite of all the 

 standing still, the retrogression, and degeneracy, there is an 

 obvious general over-all trend which can be legitimately 

 called progress in the sense that it brings about in the or- 

 ganism a greater measure of control over its environment. 

 Add to this the progression toward greater independence 

 and sensitivity and the final appearance of rising levels of 

 understanding, and the word "progress" takes on real mean- 

 ing. 



In plants the progression has been toward a higher effi- 

 ciency in the exploitation of the chemistry of the waters, 

 the air, and the soil; and, above all, in the storage of the 

 energy of sunlight. Our world is a green jewel, but it is 

 only recently in the geological sense that it has taken on this 

 useful and lovely aspect. It is now some 1,600,000,000 years 

 at least since the origin of the first cell which was capable 

 of carrying on photosynthesis, the point at which plant and 

 animal cells diverged from their common ancestor, leaving 

 to this day primitive forms which are not clearly classifiable 

 as either the one or the other. The plant took on the whole 

 burden of "fixing" the basic chemistry of life, and animals 

 became forever dependent directly or indirectly upon 

 plants. 



Plant evolution was exceedingly slow in its early progres- 

 sion. According to the record, when more than 800,000,000 

 years had passed, there were still no advanced multicellular 

 plant types, and fife was still confined to the waters. After 

 the opening of the Cambrian period of the era of ancient 

 life (the Paleozoic), the basic problem of cellular associa- 

 tion to form multicellular organisms, with division of labor, 

 was solved, and plants projected a stem above the water. 

 The invasion of the barren lands began. 



Rich premiums were offered by nature for the land 

 invasion. The ocean of the air was far richer in carbon di- 

 oxide than the waters, and minerals in almost unlimited 

 quantity were there for the taking. Certainly, the exploita- 



