264 THE AMERICAN NATURALIST [VOL. XLIII 



Nanella is a dwarf plant, but it is not distinguished by 

 its smaller size alone. 



From its first leaves to the rosette period, and through this to thd 

 lengthening stem, the dwarfs are easily distinguished from any other 

 of its congeners. The most remarkable feature is the shape of the 

 leaves. They are broader and shorter, and especially at the base they 

 are broadened in such a way as to become apparently sessile. The 

 stalk is very brittle, and any rough treatment may cause the leaves to 

 break off. ... The stems are often quite unbranched, or branched 

 only at the base of the spike. Strong secondary stems are a striking 

 attribute of the Lamarckiana parent, but they are lacking, or almost 

 so in the dwarfs. 



So far as morphological evidence is concerned, the dif- 

 ference between the above forms and elementary species 

 are not so sharp as to inspire one with much confidence 

 in the essential distinctiveness of the two classes. All 

 of these so-called varieties differ in various parts of their 

 organization. It may be said that these differences are 

 dependent through correlation upon the variation of a 

 single character, but if any one maintains that smooth 

 leaves and paler flowers, or small size, brittle stem and 

 short leaf stalks are related in this way, the burden of 

 proof is on his shoulders. If a half dozen characters in 

 different parts of the plant vary it would indeed be diffi- 

 cult, amid a considerable amount of fluctuating varia- 

 bility, to separate on morphological grounds a retrograde 

 variety from a true elementary species, especially since 

 experts are sometimes troubled in distinguishing some 

 of the elementary species from one another. Indeed, De 

 Vries admits that it is often very difficult to decide 

 whether a given form belongs to one or the other of these/ 

 two groups, but he states that in such cases we have a 

 means of testing the matter experimentally by the forma- 

 tion of crosses. Let us see, therefore, how the test of 

 crossing works out. 



In the case of the varieties of (Enothera lamarckiana 

 there is in the second generation a splitting according to 

 the Mendelian ratio when the variety is crossed with the 

 parent form, but with varieties of other forms this does 



