BOTANY 



union of corresponding genera into one family serves to give expression 

 to a real relationship existing between them. 



The evolution of a living organism from others previously existing 

 and different in form has been distinguished by Haeckel as its 

 phylogenetic development or Phylogeny. Every organism arising 

 from a like organism must, before attaining its mature state, com- 

 plete its own individual development, or, as it has been termed by 

 Haeckel, its ontogenetic development or Ontogeny. The supposi- 

 tion that the successive steps in the ontogenetic development of 

 an organism correspond to those of its phylogenetic development, 

 and that the ontogeny of an organism is accordingly a more or 

 less complete repetition of its phylogeny, was first asserted by Fritz 

 Muller, who based his conclusions on the results of comparative 

 research. 



The idea of the gradual evolution of higher organisms from lower 

 was familiar to the Greek philosophers, but a scientific basis was first 

 given to this hypothesis in the present century. Through the work of 

 Charles Darwin in particular, the belief in the immutability of 

 species has been overturned. 



Darwin is also the author of the so-called Theory of Selection. 

 In drawing his conclusions, he proceeds from the variability of living 

 organisms, as shown by the fact that the offspring neither exactly 

 resemble their parents nor each other. To establish this theory, he 

 also called attention to the constant over-production of embryonic 

 germs, by which the destruction of the greater part must inevitably 

 result. If this were not so, and all the embryos produced by a single 

 pair attained their full development, they would alone, in a few 

 generations, completely cover the whole surface of the earth. The 

 actual condition of the floras and faunas is thus maintained by the 

 restricted development of the embryos. On account of insufficient 

 space for all, the different claimants are engaged in an uninterrupted 

 struggle, in which the victory is gained by those that, for any reason, 

 have an advantage. Through this " struggle for existence," as only 

 those organisms possessing some advantage live and mature, a process 

 of enforced selection between the more fortunate survivors must result. 

 In this manner Darwin arrived at the supposition of a process of 

 Natural Selection, and confirmed his position by analogy with 

 known results obtained by experimental cross-breeding and cultivation. 

 Newly-developed peculiarities arising from individual variability must 

 be inherited in order to become permanent characteristics of a later 

 generation. Just as in artificial selection, natural selection, although 

 unconsciously, accomplishes this result. As individual peculiarities 

 may be developed by careful breeding and rendered permanent, so 

 by natural selection those qualities which are advantageous in the 

 struggle for existence become more pronounced and are finally con- 

 firmed by heredity. By the continued operation of natural selection, 



