M. J. DECAISNE ON VARIABILITY IN THE PEAB-TEEE. 



37 



bility, denies, in the most formal manner, variability in the vege- 

 table kingdom. In its opinion, specific forms are never in any 

 degree modified, and if two congeneric plants present appreciable 

 differences, however feeble they may be, these two plants are 

 from the origin of things species radically distinct. From this 

 point of view, which has found in M. Jordan of Lyons a very 

 eloquent and conscientious defender, all races and all varieties ad- 

 mitted by the other school become so many species ; and so local 

 floras are immensely increased when they have for their authors 

 men of this stamp. 



That LinnsBan botanists have made species of too great latitude, 

 by uniting under the same specific name forms which are really 

 distinct, is what I am far from contesting ; but these are errors 

 of detail which are inevitable in a first review of the general flora 

 of the world, inconveniences which experience corrects every day. 

 But we should be wrong, in my opinion, if we concluded from 

 thence the condemnation of the principle which has directed them, 

 viz. the variability of specific types. We must, however, acknow- 

 ledge that their opponents have a right to require a proof of this 

 variability, which is almost always more hypothetic than matter 

 of demonstration. It is here, in fact, that we have the, point of the 

 question ; for if what we have considered as simple alterations of 

 a more general type which is really immutable, if our supposed 

 varieties are species, in spite of their apparent affinities, we must 

 allow that our adversaries are right, and admit into our descriptive 

 catalogues all these slight species, whatever may be their number, 

 and however embarrassing a too extended nomenclature may be- 

 come. But is it in this direction that we really have improved ? 

 above all, is this the truth ? Many good authorities doubt it ; 

 not only are they afraid of seeing descriptive botany degenerate 

 into a science of words, but they ask besides, if, after all, the im- 

 mutability of forms is better proved than their variability ? One 

 way alone is open of solving the difficulty ; it is useless any longer 

 to argue, we must observe and bring forward facts ; and it is with 

 this view that I have undertaken the experiments with which I 

 have to occupy the Academy. 



In the eyes of M. Jordan* all our races and all our varieties of 

 fruit-trees, and amongst others pear-trees, are distinct invariable 

 species, remaining always identical through all possible genera- 



* Alexis Jordan, " On the Origin of different Varieties or Species of Fruit-trees 

 and other vegetables generally cultivated for the necessities of Man," 1853, Paris, 

 Builliere, p. 30, &c. 



