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H. H. BARTLETT 
vexed problem of the origin of species, must be subject to a large 
degree of reserve. Since all of the mutant Oenotheras are character- 
ized by more or less defective pollen, he thinks that the mutations are 
segregates from hybrids, and that "the mutation theory of de Vries 
appears accordingly to lag useless on the biological stage, and may 
apparently be now relegated to the limbo of discarded hypotheses." 
Fortunately for the mutation theory. Professor Jeffrey's argument is 
not sound. In the first place it must be insisted that there can be no 
such thing as a morphological test of genetic impurity. We can 
only recognize genetical impurity by genetical tests. There is a 
certain sterile variety of the sweet pea, which, according to Jeflfrey's 
pollen test, would be adjudged a hybrid. When crossed with forms 
with normal pollen it acts as a simple recessive, and like the other 
recessive varieties of this plant it has doubtless arisen by mutation. 
Bateson, who has critically studied this series of varieties, writes of, 
"... the sweet pea, a form which is beyond suspicion of having been 
crossed with anything else, and has certainly produced all the multitude 
of types which we now possess by variations from one wild species." 
Again, he states that "in spite of repeated trials, no one has yet suc- 
ceeded in crossing the sweet pea with any other leguminous species." 
In the sweet pea, then, we find pollen conditions identical with those 
which Jeffrey believes are found only in hybrids; nevertheless there is 
no reason to believe that hybridization has ever occurred in the species. 
We may turn to another case. Humulus Lupulus, the hop, is normally 
dioecious, but monoecious individuals occur now and then which can 
hardly be considered as other than mutations. Winge has recently 
studied the pollen of one of these monoecious plants, found wild and 
transplanted from the woods into his garden at Carlsberg, Denmark. 
It bore staminate inflorescences at the base of otherwise hop-bearing 
branches. Cytological study showed that pollen mother cells were 
formed which divided normally but thereafter shrivelled up without 
making the tetrad division. Winge himself points out the similarity 
between this case and that of Oenothera lata. Of all the mutations 
from Oenothera Lamarckiana, Oe. lata is the most sterile. It is gener- 
ally completely so, but two or three strains are now known which yield 
a small amount of good pollen. Monoecious hop plants likewise vary 
greatly in pollen fertility, and Winge has lately made pollinations with 
apparently quite normal pollen from a monoecious plant. Winge 
worked with the wild hop of northern Europe. Aside from geographic 
