A GRAIN OF WHEAT 39 



In order to do so it is necessary to explain to you as briefly as possible 

 the present state of biological science and the modern way of consid- 

 ering the problems relating to species. 



Modern botany, abandoning the ancient methods which depend 

 more on metaphysics and speculation than on experiments, has given 

 up the idea of discovering the origin of species by the prevalent method 

 of comparison and reasoning. The separation of forms, of varieties 

 and of species, as it is made by systematists, the herbarium specialists, 

 is based on judgment; it depends essentially on the degree of intuition 

 of the botanist who compares and draws conclusions. I do not mean 

 to say here that the methods of this science are conjectural, but I may 

 be permitted to say that it is only an outline of a science, that it is 

 provisional knowledge, a first attempt at classification. More precise 

 methods are necessary in order to resolve serious biological questions. 

 The best representatives of contemporary biological science are much 

 less hurried than their predecessors; they have acquired the conviction 

 that there is no short cut to truth. The scientific highway is paved 

 with difficulties. In this explanation, then, I shall not touch upon 

 the evolutionary speculations of Darwin or others, but shall give my 

 time exclusively to exact data. 



Contemporary biology accepts the constancy of types as a well- 

 established fact. It has discovered that this constancy is experi- 

 mentally demonstrable if the following facts, not known to Darwin 

 and his followers, be taken into account. 



Every species in its natural state, and often even in cultivation, 

 includes a large number of forms which were formerly considered 

 variations, but which, analyzed by modern methods, appear to be con- 

 stant types, all of which taken together form the Linnean species. In 

 order to discover these small constant species which ordinarily live 

 mixed together, it is necessary to segregate them. Vilmorin had 

 already recognized that unequivocal results could not be obtained in 

 the study of variation if one starts with an isolated plant or even with 

 a single seed. A single grain of wheat may be the ancestor of innu- 

 merable generations. If these isolated grains, carefully catalogued, be 

 sown separately, it is seen that they give birth to constant races or 

 lines which are called pure, because they are without mixture. To 

 evaluate these lines and differentiate them from other lines, we must 

 not consider the isolated individual, but rather note the character of 

 the descendants as a whole by means of experimental pure cultures. 

 The individuals of the same race, of the same line, may differ very 

 much according to their age, nutrition, position during the embryonic 

 or ontogenic development, but their descendants taken as a whole are 

 identical. In a pure race, the dwarfs as well as the giants give birth 



