78 BOTANICAL GAZETTE [JANUARY 
to O. Lamarckiana. The results are summarized briefly as follows: “I 
have not been able to synthesize by direct crosses, from wild stock so far 
obtained, any hybrid with all of the characters of Lamarckiana in the same 
plant, although I believe that all of the important taxonomic characters of 
Lamarckiana have been represented in some of my hybrids. ... . The resem- 
blance of my various hybrids to Lamarckiana and the parallelism of their 
behavior in the F, and F; to that of Lamarckiana give in themselves sufficient 
reasons, in my opinion, to justify the belief in its hybrid character and to 
point to the probability that this plant arose as a cross between distinct forms 
of Oenothera. Lamarckiana thus would not be representative of a wild species 
of essentially stable germinal constitution and its mutations are most simply 
interpreted as the behavior of a rid.” Prominent among the types that 
appeared in F, and again in F, and bred true in a later generation—this behavior 
constituting the similarity to the mutation habit of O. Lamarckiana—were 
dwarf forms with narrow etiolated foliage, and somewhat similar dwarf forms 
with normal green foliage. These forms occurred in approximately 1o per cent 
and 15 per cent of their respective families. Other striking forms were a semi- 
gigas type with at least 21 chromosomes, and a form similar to O. elliptica. 
With relation to a possible Mendelian interpretation of his results, DAVIS 
most troublesome problems are: (1) “the explanation of the large groups of 
warfs thrown off in the F, generations and repeated by certain plants in the 
F.,” and (2) “the explanation of the well-defined progressive evolution, exclud- 
ing the dwarfs, exhibited by these same cultures.”’ This “progressive evolu- 
tion” consisted in the appearance of F, families whose flower size ranged from 
about 1 cm. greater than that of the large-flowered parent (grandiflora), to about 
twice as large as that of the small-flowered parent (biennis), and in a corre- 
sponding increase in size and amount of crinkling of the leaves. Davis doubts 
the possibility of explaining this advance in flower size on the basis of a recom- 
bination of size factors as suggested by the multiple-factor hypothesis, because 
there was in these families no balancing group with flowers smaller than the 
small-flowered parent, and he inquires: ‘“‘What had become in these cultures 
of the factors responsible for small size?” When it is noted, however, that 
at least one F, family exhibited pronounced “‘retrogressive evolution” in flower 
size, ‘tts aienhy will be experienced by students of the inheritance of 
in interpreting Davis’ results by means of the multiple- 
factor hypothesis. The obvious suggestion is that the several F: plants tested 
had somewhat different combinations of size factors, that is, that one or both 
of the parents were heterozygous with respect to a few quantitative factors, 
a condition which could scarcely be detected under the masking effect of ordi- 
nary fluctuation without resort to a careful quantitative study of several lines 
of —_ = the plants used as parents 0 of any Byte, 
certain F, and F; culture inexplicable to Davis 
on the basis of a recombination of size ‘factors, and with this the reviewer is 
inclined to agree. The dwarfs are much smaller than the parents, the gap 
’ 
