No. 509] THE CATEGORIES OF VARIATION 267 



manifestations of heredity, the difficulty of maintaining 

 a sharp distinction between varieties and elementary 

 species on the basis of behavior in inheritance is apparent. 

 Are we to classify a six-toed cat as a variety or an ele- 

 mentary species? The variation is apparently limited 

 to a single character and it has therefore one of the marks 

 of a variety, but the variation is doubtless a progressive 

 one and not due to an awakening of a latent character, and 

 hence possesses one of the features of an elementary 

 species. When crossed some of the offspring of the 

 first generation may inherit the variation and some not, 

 and the same is true for the following generation; but 

 there is apparently no splitting according to the law of 

 Mendel. So far as our knowledge goes the situation is 

 the same in respect to polydactylism in man. 



The second volume of the Mutationstheorie, which 

 seems to have been little read by most expositors of De 

 Vries, affords several examples of irregular behavior of 

 the hybrids between elementary species which are very 

 difficult to classify. Crosses between (Enothera nanella 

 and 0. rubrinervis, for instance, the one *a retrograde 

 variety of Lamarckiana and the other a distinct elemen- 

 tary species, gave very variable results, with splittings 

 in the first and succeeding generations in very inconstant 

 ratios, and the occasional production of blends which 

 bred fairly true. We have here a curious combination 

 of the characteristics of unisexual and bisexual crosses. 



It would not be difficult to bring forward many other j 

 cases which refuse to fall within the scheme of classifica- 

 tion propounded by De Vries. There are many kinds 

 of variations which are inherited in many kinds of ways. 

 The pangen theory of the celebrated botanist has proved 

 a deceptive guide and has led its author to do scant justice 

 to many classes of facts which do not fall in line with it. 

 Hypotheses about paired and unpaired pangens have de- 

 termined De Vries 's classification of the different kinds 

 of variations and profoundly influenced his interpretation 

 of his extensive and valuable researches. The doctrine 



