320 THE LIFE OF THE PLANT 



with each other would come into existence. Something 

 of this kind was bound to take place in the natural order 

 of things, where any new form can prevail only if it is 

 more perfect than others ; in such a case it is evidently 

 bound to thrust out, to extinguish the others. Darwin 

 also points out that it is to the advantage of every being 

 to become as different as possible from its own kind, be- 

 cause the less alike are the needs of two forms the less will 

 be the struggle between them, the greater the possibility 

 of their adaptation to the same environment, without 

 any struggle whatever. Farmers have long known 

 that the same plant cannot be grown for any length of 

 time on the same field, that it is necessary to change it 

 from year to year to another place ; partly upon this 

 fact the rotation of crops is based. But what is true 

 in time appears to be true also in space : farmers also 

 know that from a certain area of land more hay can be 

 gathered when mixed grass is sown than when the grass 

 seed is uniform. Therefore it can scarcely be doubted 

 that new forms are bound to expel, to extirpate their 

 less perfect predecessors, and that of forms which arise 

 simultaneously the more strongly differentiated have 

 more chance of surviving. Thus, in varying, every 

 organic form tends to break up into subordinate groups, 

 and during the process the links between these forms are 

 lost ; so that the result is the appearance of a series 

 of divergent groups without any trace of immediate 

 transition, and yet bearing evident tokens of either very 

 close, or more remote, resemblance to one another, 

 which used to be vaguely denoted by the term affinity, 

 and which nowadays we simply call relationship. In a 

 word, the present order of the organic world, with 

 its specific and generic as well as other still larger 

 groups, is but a necessary result of their common origin 

 by means of natural selection. 



With this we close the long chain of argument which 

 contemporary biology, as represented by the great 



