182 BOTANICAL GAZETTE [SEPTEMBER 
Mutter’ deserves the credit for solving this vexing problem. -In the fruit-fly 
he discovered an essentially true-breeding hybrid race, and explained it by 
a system of balanced lethal factors. These factors assert their lethal effect 
only when they occur in the homozygous recessive condition. In this 
race of flies, two such factors are present in heterozygous condition on the 
same pair of chromosomes, the dominant members of the heterozygous sets 
being on the opposite chromosomes of the pair. Such a hybrid continues 
€ a 0) 
to the progeny. The recessives of any heterozygous set on this same 
chromosome pair will remain concealed when the stock is allowed to in- 
ree ccasional crossing-over will cause the appearance of a few (but 
in predictable frequencies) of these recessives, like the ‘‘mutants’’ thrown by 
O. Lamarckiana 
t is Siseceatlie to note that Dr Vries? himself now subscribes to 
bout 
with the charactef factor. Heterozygous combinations give good seeds, 
homozygous give sterile. If one of the two lethal factors become “vital,” 
the O. Jaeta or O. velutina mutation appears.—M. C. CouLTER. 
axonomic notes.—Miss BurLINGHAM®” has described five new species of 
Russula from Vermont and one from Massachusetts, most of which seem to 
be rare. 
ScHLECHTER™ has revised two African genera of the Orchidaceae, Schizochi- 
lus and Brachycorythis. In the former genus he recognizes twenty-five species, 
thirteen of which are new; while in the latter genus twenty-three species are 
recorded, four of which are new. He also establishes two new genera, Gyala- 
denia and Diplacorchis. 
MovrRILL,” in continuation of his investigation of Polypores, has pub- 
lished an account of some of the resupinate forms which are rose-colored, lilac, 
red, or purple. He presents twenty-six species of Poria, five of which are 
H. J., Genetic variability, twin hybrids, and constant hybrids, in 4 
case of balanced lethal factors. Genetics 3:422- . £. £018. 
9 DeVries, H., nie hue senaionsn un ghibpenwelie Artbildung. Flora 11-12: 
208-226. 1918 
bad Buxrmtasan, GERTRUDE S., Some new species of Russula. Mycologia 13: . 
129-134. pl. 7. 192 
 SCHLECHT oer Revision der Gattungen Schizochilus Sond. und Brachycorythis 
Ldl. Beih. Bot. ponent 38:80-131 
™ Murrityt, Wititam A. ,Light-coloed jeenbate Polypores. III. Mycologia 
13:83-100. 1921. 
