294 Causes and Course of Organic Evolution 



cold caused the appearance of males. Related results have 

 been obtained by others, these differing chiefly in indicating 

 that the changed conditions are only effective at certain times 

 in the life cycle. "Whitney and Shull have shown that pure 

 spring water acts on the parthenogenetic eggs of the rotifer 

 Hydatina during their growth in such a way that they develop 

 into male producing females, while eggs of females grown 

 in an infusion of horse-manure always give only female pro- 

 ducers. 



Third: Since attention was drawn to Mendel's forgotten 

 studies an abundant literature has appeared, from the time 

 of De Vries' and Correns' suggestive publications, on the results 

 of crossing experiments. Unfortunately Mendel and nearly 

 all of his followers have treated of naked-eye appearances, 

 few indeed have examined cytological details. Now, as the 

 writer's studies on plant hybrids demonstrate, one or more 

 characters from one or both parents may be inherited sep- 

 arately, owing to the absence or incompatibility of inheritance 

 of such characters from the other parent. Such phenomena 

 he termed unisexual and bisexual hybridity. But in the varied 

 cases that he studied microscopically each character inherited 

 only from one parent and reproduced in the offsprings appeared 

 only of half or nearly half the potentiality seen in that parent. 

 In other words there is no dominance or recessiveness shown 

 either in the invisible molecules or in their aggregate masses 

 that make up the inherited characters, but there is either a 

 halved inheritance or if there is incompatibility chemicallj^ 

 in fusion of the complemental parental details chemical dis- 

 integration and disappearance of the character seems to result. 



So the writer considers that most of the cases of so-called 

 "Mendelian inheritance" in plants and animals will probably 

 be found to conform to such conditions, when they have been 

 studied microscopically, and still more microchemically. 

 But even in the case of macroscopic details very loose state- 

 ments have been made. Thus the writer was recently shown 

 an ear of white and of black corn along with a so-called "black" 

 ear, obtained by crossing of the two parents. When the three 



