SOME PRINCIPLES OF PLANT EVOLUTION 489 



ation under different conditions, as well as the causes of these 

 variations, and the natural methods by which certain ones sur- 

 vived while others perished. To him we owe the elaboration of 

 the theory of " Natural Selection " as one of the important 

 natural laws in the origin of species, since selection acts in the 

 direction of the preservation of the best forms from which new 

 species are differentiated. 



Darwin's most important work was the " Origin of Species," 

 first published in 1859. This work was the result of twenty 

 years of careful study and observation on the variations of plants 

 and animals, both wild and domesticated, and the causes which 

 led to improvement under the control of man, as well as in a 

 state of nature. His great work here consisted in the vast amount 

 of evidence which he presented in favor of the natural origin of 

 species, that species vary, and where these variations are bene- 

 ficial, natural selection preserves the forms which possess them 

 while it destroys the others. 



661. Mendelism, or mendelian hybrids. Gregor -Mendel, 

 born in Briin, Austria, in 1822, discovered the law governing this 

 kind of hybrids. He was a monk, and afterward became the 

 Abbot of Brun. He discovered this law during his experiments 

 on plant hybridization, and published an account of this in the 

 Natural History paper of his town. This work did not become 

 widely known at the time, and the paper was only recently redis- 

 covered and published, so that it became accessible to all workers 

 in plant breeding.* It was a very interesting discovery as well 

 as being of great importance to the plant breeder. Mendel 

 worked chiefly with peas. Two examples will be given here to 

 serve as illustrations of the principle. 



He selected two varieties of peas which differed in one being 

 tall and the other a dwarf. These were cross pollinated. The 

 seed from the cross was sown the following year, and all the 

 progeny resembled the tall parent, i.e., all of the first generation 

 of hybrids were tails, and no sign of the dwarf character could 



* See Bateson, Mendel's Principles of Heredity; also Punnet, R. C., 

 Mendelism. 



