527 



show simple segregation. The mutation will appear for 

 the first time in iM per cent, of the progeny. De Vries has 

 recently reported that the dwarf mutation from (En other a 

 gigas is of the simple recessive Mendelian type. We must 

 believe, in a case of this kind, that the factor whose modi- 

 fication results in dwarf ness is present in all gametes. It 

 does not follow, however, that the gametes are all equiva- 

 lent with respect to the factors for other characters. 



In connection with the discussion of Davis's hybrids 

 which resembled (Enothera Lamarckiana I mentioned that 

 the mutability shown by them was probably inherited 

 from one or both parents. There seems to be some scepti- 

 cism about the inheritance of mutability as a character. 

 Much of my own experimental work of the last two years 

 has involved (E. pratincola, a mutable species which has 

 already been refered to several times. There is another 

 species from the same locality which is rather closely 

 allied to (E. pratincola, but differs in enough regards so 

 that the hybrids between them can be studied with great 

 satisfaction. The second species, (E. numismatica, is im- 

 mutable, as far as my experience extends. At any rate it 

 is very much less mutable than (E. pratincola. The cross 

 (E. pratincola X (E. numismatica gives twin hybrids, one 

 of which is exactly like the pistillate parent except in one 

 minor pubescence character. The reciprocal cross, <E. 

 numismatica X CE. pratincola, is to all outward appear- 

 ances the same as the pistillate parent. We have here a 

 most striking case of matroclinic reciprocal hybrids. I 

 am inclined to believe that most of the differences between 

 the two species reside in the a gametes and that the p 

 gametes are essentially similar. In accord with this hy- 

 pothesis nothing could be more interesting than to find 

 that the pratincola-like hybrid is mutable, and produces 

 the same types of mutations that (E. pratincola itself does. 

 This result, it seems to me, is of the highest significance. 

 It indicates that the germ plasm of (E. pratincola is in a 

 labile condition, and that this condition is not modified 

 when a zygote is formed by the fusion of its a gamete with 

 the p gamete of a different and stable, or at least relatively 



