2 BOTANY 



development or PHYLOGENY. He termed the series of changes 

 passed through by a living being in attaining its mature condition, 

 its ontogenetic development or ONTOGENY. The supposition, 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 compk-te 

 repetition of its phylogeny, was asserted by FRITZ MULLER ( 2 ), 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 last century. Through the work of 

 CHARLES DARWIN ( 3 ) in particular, who accumulated evidence for a 

 reconsideration of the whole problem of organic evolution, the belief 

 in the immutability of species has been overturned. 



DARWIN is the author of the THEORY OF SELECTION. In drawing 

 his conclusions, he proceeded from the variability of living organisms, 

 as shown by the fact that the offspring neither exactly resemble 

 their parents nor each other. Further, he called attention to the 

 constant over-production of offspring, the majority of which must 

 inevitably be destroyed. 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. 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 " a selective process goes on 

 among the characters appearing in individual variations, and those 

 which under the conditions of life are in any way advantageous tend 

 to be preserved. In this manner DARWIN arrived at the supposition 

 of a process of NATURAL SELECTION, which is the essential of his 

 theory. Newly developed peculiarities arising from individual vari- 

 ability must be inherited in order to become permanent characteristics 

 of a later generation. DARWIN sought in the experience of breeders 

 evidence that such characters are inherited. The breeder selects indi- 

 viduals presenting any desired characters for the purpose of breeding, 

 and has thus formed the races of domesticated animals and cultivated 

 plants. These have often departed so widely from their wild 

 ancestral forms that the latter are not certainly known. Just as 

 in artificial selection, natural selection, although unconsciously, ac- 

 complishes 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 confirmed by heredity. By 

 the continued operation of natural selection, organisms must result, 

 which are, in the highest degree, fitted and adapted to their 

 environment. In this way the theory of selection seeks to explain as 



