432 The Living Plant 



be can obtain such a race is by watching for plants which naturally 

 exhibit an inborn short-stemmed or long-stemmed variation, re- 

 spectively, selecting them out and propagating them ; the short- or 

 long-stemmed character will appear in their descendants, and by 

 consistent repetition of selection of the same variation for some 

 generations, a race capable of perpetuating the short- or long- 

 stemmed character can be obtained. The fact, then, that innate 

 variations are hereditary is the most important fact about them 

 from the point of view of plant improvement. 



There is one other point about the heredibility of variations 

 which we must note at this place. It was Darwin's view that 

 variations rise and fall, or flash, as it were, across several genera- 

 tions, and, unless preserved by selection, sooner or later die out. 

 But modern studies are showing that variations appear linked 

 several together in those mutants, biotypes, or elementary species 

 which we have already considered in the preceding chapter, 

 while, once in existence, they persist indefinitely. What then, 

 on the newer view, is the gardener doing when selecting vari- 

 ations for the improvement of plants? Simply this, — he is 

 isolating the desirable biotypes from among the less desirable 

 kinds making up the great mixture of which any crop consists. 

 Thus a field of Corn or Wheat consists of a great number of bio- 

 types, and hybrids thereof, from which the best kinds can be 

 selected and propagated. But, on the newer view, once the best 

 biotypes are isolated, no further improvement is possible, while 

 the selection of variations should permit an indefinite, or at least 

 much larger improvement. Experience is certainly showing the 

 truth of the modern view in many cases, though the accumulation 

 of single small variations seems equally clear in other instances. 



A second great fact about variation is this, — it is spontaneous, 

 which m.eans that it appears without any determinable reference 

 to any features of the surroundings. But while the surroundings 

 do not in any known way determine the nature of variations, they 

 certainly do promote them, both in number and intensity, as 



