PLANT HYBRIDIZATION BEFORE MENDEL 271 



Macfarlane uses the term "unisexual heredity" to designate the 



cases in which 



". . . structures found only in one parent, and with no corresponding 

 counterpart in the other, are handed down, though reduced by half." 

 {ib., p. 273.) 



In this connection he makes a rather interesting comment : 



"Now it has been repeatedly noticed that when a species varies from 

 the normal, it seldom does so in only one point or structural detail, but 

 a certain variation-wave, so to speak travels through the entire organism, 

 giving it that combined set of characters which make it rank as a sub- 

 species." {ib., p. 274.) 



As what he terms "bisexual heredity," Macfarlane designates 



such cases as Ribes culverzvelhi, 



". . . in which the simple hairs of R. grossularia and the oil-secreting 

 peltate hairs of R. nigrum are both separately reproduced, though about 

 half as large as those of the parents." (p. 274.) 



The case of the similar inheritance of epidermal hairs in Saxi' 



fraga and Carduus hybrids is also cited. It is interesting to note 



that Macfarlane reports that he knows of no cases 



". . . where internal elements or tissue-masses are thus separately re- 

 produced" (p. 274), and he further notes that "all the hybrids in which 

 the above has been observed are derived from parents considerably re- 

 moved in systematic relationship, and the incompatibility of blending the 

 diverse types of hairs probably explains their appearance as separate 

 growths." (ib., p. 274.) 



He says further : 



"But the general principle here illustrated on an exaggerated scale is 

 that the offspring of two parents may inherit from each diverse peculiari- 

 ties which, instead of blending evenly, retain their separate individuality. 

 Future experiment and observation alone will decide for us whether 

 these can be passed down through two, three, or more generations, and 

 till we have the evidence it would be impossible to generalize." {ib., 

 p. 274-) 



A theoretical attempt at the resolution of the behavior of the 



characters in a hybrid into their factorial components is further 



enunciated : 



"if we view a fertilized egg of any plant, which is about to segment to 

 form an embryo, as being not merely a chemically complex nucleated 

 mass of protoplasm, but as a microcosm in which the orderly-arranged 

 molecules of the conjugated male elements have so exactly fitted into 

 and become united with corresponding molecules of the female element, 

 that after conjugation, coordinated groups of molecules are set apart as 

 stem-producers, root-producers, leaf-producers, and hair-producers, we 

 will have done much to clear away obstacles. But physically there is 



