THE MUTATION THEORY : A CRITICISM. 



147 



leaved inland ones of many genera, or the non-spiny pears and plums 

 of our gardens were latent in the wild pear and sloe, &c. This con- 

 ception of latency is thus easily reducible to a reductio ad ahsurdum. 



Professor de Vries of course lays stress on the constancy of his 

 forms, but that is a result to be expected, for he apparently grew them, 

 generation after generation, in the same conditions in which they arose ; 

 and so the " direct action " of the same soil acted on the offspring in 

 the same way as on the parent. It is a significant fact that the two 

 kinds he found in the sandy soil of Hilversum (0. laevifolia and 0. brevi- 

 siylis) never appeared in his cultivations, though they seem to have 

 proved constant when he grew them in the garden. This would be 

 in accordance with M. E. A. Carriere's experience, who writes; 

 " Faisons remarquer que les diverses combinaisons faites pour per- 

 petuer les vari^t^s, ou pour en obtenir de nouvelles, reposent sur cette 

 loi generale que, dans la nature, toiit tend d se reiproduire et meme d 

 s'^iendre, que par consequent les modifications peuvent nou seulement 

 devenir hereditaires, mais qu'elles peuvent encore servir de moyen pour 

 arriver a d'autres modifications, a etendre et a multiplier de plus en plus 

 les series ty piques."* 



Professor de Vries would draw the distinction between a " muta- 

 tion " and a " variety " by limiting the latter to a single character, 

 but such is not the view of any systematic botanist. Open Hooker's 

 Student's Flora at any page, the first variety that meets the eye will 

 be found to be only recognizable by more than one character, so that in 

 this respect there is no difference between a mutant and a variety. 



The suddenness of the appearance of the changes in a plant is a 

 normal or general feature, provided the new environment is markedly 

 different from that of the parent. A change to fleshiness at once occurs 

 if plants be watered with a weak solution of salt; and, conversely, 

 maritime plants may lose it if raised from seed in sand. Aquatic plants, 

 as Ranuncuhis heteropJiyllus, grown by seed on land become very 

 different plants, anatomically, for they are now in adaptation to air; 

 but if they be transferred to water before they are fully grown the new 

 leaves will be of the aquatic type, the aerial type perishing. M. Car- 

 riere raised spindle-rooted and turnip-rooted radishes in a loose and 

 compact soil, respectively, from seed of the wild Eaphanus Raphani- 

 strum; and these forms are now hereditary. 



Consequently it is difficult to^ accept Professor de Vries 's assertion 

 that " the laws of mutability are quite different from those of individual 

 variation. '"f The degrees, if any, of difference in forms between 

 mutations and varieties seem to be inappreciable, while those of con- 

 stancy or inconstancy are the same; they both appear stiddenly — that 

 is to say, while the seedling is growing to maturity, it responds to 

 the new conditions of life, and if the new structures it puts on render 

 it more suitable they are adaptations. If they turn out unhealthy, as 

 in Professor de Vries 's " species, " it proves that the environment is not a 



* Prodnciion et Fixation des Varietes dans les Vegitaux, p. 9, 1865. 



t p. 6. 



L 2 



