260 THE AMERICAN NATURALIST [VOL. XLIII 



behave in quite different manner, when subjected to crossing experi- 

 ments, and the hope is justified that some day crosses may become 

 the means of deciding, in any given instance, what is to be called 

 species, and what variety on physiological grounds. 



When varieties are crossed with the parent type the 

 character that is active in one or the other of the forms 

 will usually be patent in the first generation of offspring. 

 In the second generation there is, according to De Vries, 

 a segregation of characters which takes place in con^ 

 formity to Mendel's law. Ordinary sugar corn, for ex- 

 ample, differs from the usual type in having a part of 

 the starch replaced by sugar in the kernels, which conse- 

 quently become wrinkled when dry. When these two 

 forms are crossed the active character of starchy kernels 

 is present in all the members of the first generation. In 

 the second generation there is a segregation of these 

 characters, one fourth of the offspring being wrinkled 

 kernels, and three fourths smooth ones. Approximately 

 one third of the latter produce only smooth kernels in 

 subsequent generations, while the other two thirds split 

 up again in the expected Mendelian ratio. 



In the crossing of varieties it is possible, according to 

 De Vries, for all the corresponding characters of the two 

 forms to become paired. As the distinguishing feature 

 of the variety is the latency or patency of one or more 

 characters, these characters "will unite as well as though 

 they were both active or both dormant. For essentially 

 they are the same, only differing in their degree of ac- 

 tivity. From this we can infer that, in the crossing of 

 varieties, no unpaired remainder is left, all units com- 

 bining in pairs exactly as in ordinary fertilization." As 

 the varieties differ only in the dominance or latency of 

 certain characters, offspring obtained through crossing 

 them differ only in the same way. For such unions De 

 Vries gives the name "bisexual crosses," inasmuch as 

 there is "complete bisexuality, all unit characters com- 

 bining in pairs. ' ' 



In the crossing of the elementary species of (Enothera 

 De Vries found that in the first generation there was a 



