220 EXPERIMENTAL EVOLUTION LECT. 



Some mutilations react on the process of fructifica- 

 tion, if it be true that by cutting through the medulla of 

 a grape-vine stem, grapes are obtained which contain 

 no seeds. The fact has been often spoken of for 

 at least 1,900 years, as ancient Romans practised it, 

 according to trustworthy witnesses, such as Columella, 

 Camulogen, and Pliny. 1 At all events the experiment 

 is worth trying, and some interesting facts might be 

 derived from it. 



Colour variations may be experimentally deter- 

 mined through changes in environment. Moleschott 

 has observed that in pure oxygen no black pigment is 

 generated in the skin of frogs, and the coloration of 

 birds' eggs sometimes varies with the amount of light 

 to which they are exposed. These facts are enough 

 to point the way to many interesting experiments. 



We can also produce changes in sexuality, since we 

 know that the want of suitable depositing ground for 

 trout, is, according to Barfurth, followed by degenera- 

 tion and permanent sterility, or at least by the 

 production of weak forms. In many cases also, defi- 

 cient nutrition of parents determines predominant 

 maleness in the progeny, and Giard has shown that 

 castration parasitaire, as he calls it, that is the presence 



1 Cf. Revue Horticole, 1884, pp. 6 and 219; Couverchel, Trait* des 

 Fruits, 1839 ; Columella, De Arboribus, and also Olivier de Serres, 

 who knew of the process, but denied its efficacy. 



