84 HEREDITY AND EVOLUTION IN PLANTS 



the appearance of life and the present condition of living 

 things. 



The major problem of botany is to record, in order, the 

 evolutionary steps that have culminated in the present con- 

 dition of the plant world. 



Organic evolution means that, after the first appearance 

 of life, all living things, plant or animal, have been 

 derived from preexisting living things, in other words, that 

 the present method of formation of living things, by the 

 reproduction of organisms already existing, has always 

 been the method — "Omne vivum ex ovo" (all life from an 

 egg), "omne vivum e vivo" (all life from preexisting life). 



74. Method of Evolution. — To recognize that evolution 

 is the method of creation still leaves unanswered the im- 

 portant question as to the method of evolution. By what 

 process was the gradual development of the living world 

 accomplished ? Various hypotheses have been elaborated 

 in answer to this question. We can here only briefly 

 outline three of the most important ones. 



I. Agassiz's Hypothesis. — The great teacher and student 

 of nature, Louis Agassiz, believed that the vast array of 

 plant and animal species, past and present, had no material 

 connection, but only a mental one; that is, they merely re- 

 flected the succession of ideas as they developed in the 

 mind of the Creator, but were not genetically related to 

 each other. "We must . look to some cause outside 

 of Nature, corresponding in kind to the intelligence of 

 man, though so different in degree, for all the phenomena 

 connected with the existence of animals in their wild 

 state. . . Breeds among animals are the work of man: 

 Species were created by God."^ 



• Agassiz, L. "Methods of Study in Natural History," Boston, 1893, 

 pp. 146, 147. 



