132 
CARL D. LA RUE AND H. H. BARTLETT 
De Vries^ would apply the term heterogamous. It has frequently 
been found that crosses of the Oenotheras differ strikingly according 
to the direction in which the cross is made. Often the reciprocal 
hybrids from the same two parent plants are as unlike as the parents 
themselves. De Vries has attributed such results to a difference in the 
hereditary qualities of the male and female gametes, and has suggested 
the term heterogamy for the condition of species in which such a 
differentiation of gametes is found. There is much unpublished evi- 
dence at hand which tends to show that heterogamy may exist in 
some species without a sharp restriction of either type of gamete to 
the eggs or sperms and on this account we shall use the term "heter- 
ogamy" with no implication that the non-equivalent gametes may 
not exist on both the male and female sides. The conception of 
heterogamy so modified as to apply to results that have been obtained 
in our experiments has been published^^ in advance of the data which 
suggested the modification. 
Let us assume (i) that a heterogamous species such as Oe. Reynold- 
sii normally produces two types of non-equivalent gametes, which 
may be designated as a and respectively; (2) that the a gametes 
carry most of the characters by which specific differentiation is effected ; 
(3) that mutation occurs through the modification of a gametes, which 
thus become a , a" , a" , etc. Applying this conception to the par- 
ticular case in hand, let us think of f. typica as the zygote cejS, mut. 
semialta as a'/S, mut. dehilis as a."^, and mut. hilonga as a'"^. The 
conditions imposed by the results of the various crosses are satisfied if 
f. typica — > a eggs + jS sperms, 
mut. semialta — > a eggs + /3 sperms, 
mut. dehilis -> a" and jS eggs + /3 sperms, 
mut. hilonga — > a^' and ^ eggs + a" and sperms. 
Since the various forms are determined by the a gamete, all mutation 
crosses must of necessity show matroclinic inheritance, except those 
involving mut. hilonga, for this one form is the only member of the 
series that produces any male a gametes. In order to be functional, 
male a gametes must fuse with female /3 gametes, which are produced 
only by mut. dehilis. Therefore the cross dehilis X hilonga is the 
only one that yields both the maternal and paternal types. It will 
^ De Vries, Gruppenweise Artbildung, pp. 30-32. 
^° Bartlett, H. H., The Status of the Mutation Theory, with Especial Reference 
to Oenothera, Amer. Nat., 50: 513-529. 1916. 
