THE MUTATION THEORY 113 



first the fact that muricata 9 X dwarf nanella c? gives about 

 50 per cent, laeta and about 50 per cent, of velutina. 

 As regards Velutina it was shown that: 



Tails, Dwarfs, 



per cent. per cent. 



I. Velutina selfed gave 38 62 



Velutina 9 X dwarf nanella c? gave 39 61 



do. X do. gave 49 51 



do. X dwarf c? derived from velutina gave 43 57 

 3. Dwarfs X velutina cf gave all dwarfs 



The three experiments taken together prove, as de Vries says, 

 that the ovules of velutina are mixed, tails and dwarfs, and that 

 the pollen is all dwarf. The condition is almost the same as 

 that of the Stocks. It may be noted also that in the Stocks the 

 egg-cells of the "double" type are in excess, being approximately 

 9 to 7 of the "single" type, but de Vries regards the two types 

 in velutina as probably equal in number. The figures (169 : 231) 

 rather suggest some excess of the recessives, perhaps 9:7, and 

 the point would be worth a further investigation. 



As regards laeta, by self -fertilisation no dwarfs were produced, 

 but in all other respects it behaved almost exactly like velutina. 

 The ovules are evidently mixed tails and dwarfs, and whether 

 fertilised by dwarfs or by the pollen of velutina, which is already 

 proved to be all dwarf, the result was a steady 50 per cent, of 

 tails and 50 per cent, of dwarfs. The pollen of laeta used on 

 dwarfs gives nothing but dwarfs, and in three series of such ex- 

 periments 226 dwarfs were produced. 



We are thus faced with this difficulty. Since the egg-cells of 

 laeta are evidently mixed, tails and dwarfs, and the pollen used 

 on dwarfs gives all dwarfs, why does not self-fertilisation give 

 a mixed result, tails and dwarfs, instead of all tails? De Vries 

 regards the result of self-fertilisation as showing the real nature 

 of the pollen, and declares it to be all tails, while he represents 

 the behaviour of the same pollen used on dwarfs by stating that 

 in these combinations the dwarf character dominates. This 

 does not seem to me a natural interpretation. I should regard 

 the pollen of laeta as identical with that of velutina, namely dwarf, 

 and I suspect the difficulty is really created by the behaviour of 

 laeta on self-fertilisation. Until a proper analysis is made in 



