8 Plant-Breeding 



the cause of much of the variation in plants, since differ- 

 ences in plants were positively injurious if it were possible 

 for the conditions of environment to be the same. 



Species-formation. If no two plants are anywhere 

 alike, then it is not strange if now and then some de- 

 parture, more marked than common, is named and becomes 

 a garden variety. We have been taught to feel that 

 plants are essentially stable and inelastic, and that any 

 departure from the type is an exception and calls for im- 

 mediate explanation. The fact is, however, that plants 

 are essentially unstable and plastic, and that variation 

 between the individuals must everywhere be expected. 

 This erroneous notion of the stability of organisms comes 

 of our habit of studying what we call species. We set 

 for ourselves a type of plant or animal, and group about it 

 all those individuals that are more like this type than 

 they are like any other, and this group we name a species. 



Nowadays, the species is regarded as nothing more than a 

 convenient and arbitrary expression for classifying our 

 knowledge of the forms of life, but the older naturalists 

 conceived that the species is the real entity or unit in 

 nature, and we have not yet wholly outgrown the habit of 

 mind which was born of that fallacy. Nature knows 

 little about species ; she is concerned with the individual, 

 the ultimate complete and working unit. This individual 

 she molds and fits into the opportunities of environment, 

 and each individual tends to become the more unlike its 

 birthmates the more the environments of the various in- 

 dividuals are unlike. 



We must consider, therefore, as a fundamental concep- 

 tion to the discussion of the general subject before us, the 



