157 



its mother. When both parents possess similar characters the 

 offspring will naturally tend to strongly resemble the mother 

 plant, although this depends to some extent on the conditions 

 under which the young plant develops, but if this is not the 

 case the results of the cross may be very various, as has been 

 noted in the remarks on hybrids. We have also seen that, 

 when a hybrid form is repeatedly crossed with one of its 

 parents, it tends to quickly revert to that parent form, and in 

 this way sexual reproduction may help to eliminate new vari- 

 ations and to keep species constant in nature. A character 

 which may appear to have been lost is frequently found to be 

 really only dormant, or latent, and although it may be 

 inherited in this state during many generations it is always 

 likely to reappear and again become active. This phenomenon 

 of the reappearance in a plant of an ancestral quality which 

 has been latent in its parents is termed atavism. 



139. We have seen above that a Selection. 



large proportion of all living organisms which come into 

 existence must perish prematurely and that in nature those 

 which are best adapted to the conditions under which 

 they exist are selected, or chosen, as it were, by nature, 

 and survive, while the remainder are rejected and perish. This 

 Survival of the Fittest, therefore, is seen to be the result of the 

 so-called Natural Selection. Selection has been well likened to a 

 sieve, only those individuals which possess the necessary 

 qualifications are able to remain and are selected, while the 

 remainder pass through the sieve and are rejected. It is advis- 

 able to distinguish two kinds of selection, viz. that which 

 selects a particular sub-species, or race, from among other sub- 

 species and races, and that which selects particular individuals 

 within one and the same sub-species, or race. An example of 

 the first occurs when, in a field of wheat, a single sub-species is 

 selected from among the others growing with it and is then 

 isolated and separately propagated. The same thing occurs in 

 nature when, from a number of mutations, only those which are 

 best adapted to the conditions of life are selected and survive, 

 while the others perish. In addition to this, however, we know 

 that, within one and the same sub-species, or race, there is 

 always fluctuating variability that no two individuals are ever 

 exactly alike and that the same quality or character is 

 exhibited in different degrees by different individuals. Hence 

 it might be inferred that breeding entirely from those indivi- 

 duals which exhibit a desirable character in a marked degree 

 would result in the production of similarly characterised 



