420 BOTANICAL GAZETTE [MAY 
already explained, it differs mainly in the conception of the first 
origin of O. Lamarckiana. RENNER considers this species to be a 
hybrid between two previously existing types, corresponding to 
laeta and velutina, and sees in this hybrid condition the cause of its 
mutability. The analogy with O. grandiflora leads us, however, to 
consider this ‘‘hybrid condition” not as the cause but as a result of 
the mutability. Elsewhere I have shown that his conception leads 
to contradictions and requires too many additional hypotheses, 
even without considering the analogy with O. grandiflora (4). A 
detailed criticism of RENNER’s views from this latter standpoint, 
however, must be postponed until another opportunity. 
Summary 
1. Oenothera grandiflora Aiton from Castleberry, Alabama, splits 
in my cultures in every generation into two types. One of them 
consists of strong, green plants of the parent type; the other of 
weak, yellow individuals, of which only a few are vigorous enough 
to flower and ripen their seeds. This weak type is called O. grandi- 
flora mut. ochracea. 
2. Besides these it produces other mutants in the ordinary pro- 
portions of o.1-1 per cent, namely, mut. Jorea with almost linear 
leaves and mut. gigas with 28 chromosomes and the corresponding 
stoutness of all its organs. These two types are constant from 
seed, but the gigas keeps on mutating into Jorea and ochracea. 
3. The crosses among O. grandiflora, O. ochracea, and O. lorea 
show that these forms are isogamic, the pollen carrying the same 
hereditary qualities as the egg cells. 
4. O. grandiflora yields twin hybrids with the same species which 
produce twins in their combinations with O. Lamarckiana. The 
female organs of O. biennis, O. syrticola (muricata), O. suaveolens, 
the pollen of O. biennis Chicago, and both sexes of O. Cockerellt split 
O. grandiflora into laeta and velutina, whereas the cross O. biennts 
Chicago X grandiflora yields the twins densa and Jaxa. The twins 
appear, on the average, in about equal numbers. This splitting 
fails when the crosses are made with mut. ochracea instead of 
O. grandiflora. Their progeny is uniform and corresponds, so far 
as investigated, to the /aeta among the twins. 
