159 



best results are, as a rule, obtained by selecting not those 

 individuals which exhibit the best visible characters, but those 

 plants which are found to produce the most desirable offspring ; 

 in other words, the value of a plant is gauged not by its visible 

 attributes but by its power to transmit desirable qualities to its 

 descendants. For this purpose the seeds of each individual are 

 sown separately and, to obtain an average value for the offspring 

 of each individual, 100 seedlings are carefully examined and their 

 qualifications considered. Only those groups which contain the 

 greatest number of desirable individuals are then selected for 

 further cultivation. This method is based on the idea that a 

 single plant, or even a few individuals, may owe their qualifica- 

 tions not to any inherited attribute but to extraordinarily 

 favourable conditions to which they have been subjected during 

 their own life-time. Although great improvements have been 

 wrought on the lines indicated above, no permanent improve- 

 ment has, up to date, been effected and no new and constant 

 race has been produced. Experience hitherto gained has shown 

 that whatever standard of selection is adopted, a limit to the 

 improvement effected is soon reached beyond which it is impos- 

 sible to go, and, further, that when a desirable degree of 

 improvement has been reached, this can only be maintained by 

 continued selection, for if selection ceases, the race soon reverts 

 to its original type. 



140. Linnaeus, the most famous of Origin of 

 the early botanists who worked at classification, thought t 

 each species had been separately created at the beginning of the 

 world and that the individuals of a species were only capable of 

 producing other individuals like themselves, i.e. that existing 

 species had remained unchanged from the creation. Charles 

 Darwin, however, subsequently proved thatthis was not the case 

 and that, from one species, other and totally distinct species 

 could arise in the progress of time. The theory of evolution in 

 the animal and vegetable kingdoms is now universally accepted 

 as correct, as is also the fact that this evolution is mainly 

 dependent on two factors, which are : 



(1) the variability of living organisms, and 



(2) the struggle for existence, owing to which only those 



organisms are able to survive which are most per- 

 fectly adapted to the conditions under which they 

 exist, which are best able to withstand unfavourable 

 conditions of soil, or climate and which can best 

 hold their own against other injurious organisms. 



