II DWARFING AND STERILITY 75 



occurs in the environment/ M. A. Roujon, of 

 Clermont-Ferrand, 1 by selecting the central, smaller 

 seeds of dwarfed plants of Helianthus annuus, Calen- 

 dula arvensis, and Zea rnais^ has been able to obtain 

 very small individuals of these three species. But the 

 most important fact, among those he has observed, 

 is that while the dimensions of the plants decrease, 

 their fertility is much impaired : the number of seeds 

 which are produced becomes smaller, and dwindles 

 down to 4, 3, 2, i, only, and finally no more seeds are-' 

 produced : a condition of absolute sterility is induced. 

 This concomitant sexual variation is of great import- 

 ance, of course, in showing that when dimensions vary 

 they are not alone variable ; there are other variations 

 which accompany the differences of dimensions. 



One fact must be noticed concerning the point 

 which is now under consideration. It is the fact that 

 while we can easily, through a number of methods,! 

 induce unfavourable conditions, it is much more 

 difficult to induce favourable circumstances which, 

 lead to a better development. The advance of know- 

 ledge, however, may be expected to yield results 

 which shall prove more satisfactory, but we perceive 

 the difficulty of progress through the difficulty we 

 experience when we wish to maintain any natural or 



1 De quelques Variations considerables observees chez les Vegetattx. 

 Journ, d'Ifist, Nattirelle de Bordeaux, t, iii., 1884, p. 156. 



