General Introduction n 



extension of our scientific knowledge of the vegetation 

 of the globe.' 1 



The trend of the main line of thought, then, in the years 

 immediately preceding i860, was clearly if not very 

 emphatically, in the direction of the rejection of the old 

 dogma of the constancy of species and the substitution of 

 something more plastic and more in harmony with current 

 discoveries. The way was thus in some sense prepared 

 for the work which, from its bold generalization based on 

 years of skilful research and matured reflection, made the 

 years 1859 and i860 a most prominently marked epoch 

 in botanical research. On July 1, 1858, papers were 

 communicated to the Linnean Society of London, ' On the 

 tendency of species to form varieties and on the perpetua- 

 tion of varieties and species by natural means of selection,' 

 submitted jointly by Charles Darwin and A. R. Wallace, 

 which embodied the first statement of the new views, and, 

 in the next year appeared the monumental work of the 

 former — The Origin of Species by Natural Selection — 

 which was destined almost at once to revolutionize the 

 methods and direction of biological research, substituting 

 finally a definite plan of investigation for what had been up 

 to that time almost purely empirical. At once Phylogeny 

 as a definite line of inquiry, stood out before the thinker, 

 and a new principle appeared established. Physiological 

 problems assumed pre-eminence almost at a bound ; the 

 inquirer saw before him living individuals engaged in the 

 struggle for existence and the propagation of their kind, 

 contending partly with each other, partly with their 

 surroundings, and almost for the first time he recognized 

 the needs of life as the central point of interest, while 

 details of structure acquired a new importance as they 

 were interpreted in the light of this inevitable contest and 

 turmoil. Physiological needs in the presence of environ- 

 1 British Association Reports, Belfast, 1874. 



