212 BOTANY PART i 



2. Darwinism ( 104 ' 106 ). DARWIN starts from the fact that the 

 limited conditions for life on the earth do not permit of unlimited 

 increase in the number of organisms. Nearly every living being 

 produces during its individual existence so many germs that were all 

 to grow the whole earth would in a short time be overpopulated. 

 That so few descendants of an individual survive is due to many 

 being destroyed at all stages from the germ cell onwards. They are 

 overcome in the STRUGGLE FOR EXISTENCE with the environment, in 

 which other organisms of the same or different species are included. 

 Were all the offspring alike, accident only would decide which should 

 survive, and such accidents do play a great part. Since, however, 

 inheritable differences occur among the offspring, those individuals 

 will as a rule be favoured in the struggle for existence which by 

 their peculiarities are capable of maintaining themselves, or are more 

 capable than the others in the particular situation to which chance 

 has brought them. Thus a process of selection (NATURAL SELECTION) 

 comes about. If, further, the selected variants hand on their 

 properties to their descendants, and the variation and the struggle 

 for existence is repeated, the process must lead to the selection of 

 still better adapted forms. Organisms may arise with any sort of 

 characters, useful, indifferent, or harmful. Since, however, those 

 with injurious qualities promptly disappear, those that remain are 

 better adapted than those that perish. Usefulness which was not 

 explained by Lamarckism (where the useful capacity of reaction in 

 relation to new conditions of the environment was assumed) comes 

 about according to Darwinism from the preservation of new inheritable 

 properties which contribute to the success of the organism in the 

 struggle for existence. It is in this that the great advance made by 

 DARWIN'S theory, as compared with Lamarckism, consists. It is 

 supported, as has been seen, by the observations hitherto made on 

 the origin of new inheritable characters in organisms, although the 

 assumptions of Darwinism leave various difficulties to be overcome. 



