1918] DEVRIES—MASS MUTATIONS 403 
seed, which germinated in 1916. Unfortunately this seedling was 
attacked by some disease, but it flowered in September with the 
buds, flowers, and pollen of a pure gigas, and showed 28 chromo- 
somes in the nuclei of its roots in preparations made for me by my 
assistant Mr. C. VAN OVEREEM. 
O. hybr. mut. nanella were dwarfs like the hybrid dwarfs of 
O. Lamarckiana. They appeared in the second generation of /utea 
specimens from crosses between O. LamarckianaXlorea and O. 
lorea Xnanella. 
I made my crosses in different years and cultivated about 30 or 
60 offspring of each. I counted them in July at the beginning of 
the flowering period, when the characters were most sharp and no 
doubtful specimens remained. I made one cross first in 1913, and 
the others in the two following years, so as to have cultures of the 
second generation along with the trials of the first. This, of course, 
is the best means of thoroughly comparing the types during the tests. 
The size of the cultures is too small to give reliable proportions 
for each of them. Their aim is to show that the three types arise 
from every combination without exception, and that the mutants 
arise only occasionally. The size of the whole group, however, is 
large enough to warrant the reliability of the average proportions. 
In calculating these I have reckoned the gigas plants with the ovata 
and the /utea respectively, on the ground of their general appearance. 
The contraria were calculated separately. No other types occurred, 
especially no lorea, no ochracea, no dwarfs, and none of the special 
types afforded by later generations. 
Some details may be given now concerning these experiments. 
O. grandifloraXO. Lamarckiana.—Cross of 1914 between two 
specimens of my races. I cultivated 60 offspring until July, but 
retained only one-half of them during August and Septembér. This 
half had been planted on a bed in April, before the distinguishing 
marks were clear. In July I counted 30 ovata, 11 lutea, and 18 
brunnea, but could not distinguish the contraria. For this reason 
only the results of the counting on the bed in August have been 
given in table V. The three types were exactly the same as in the 
other cultures. Of each of them one plant has been fertilized in 
order to study their second generations in 1916. 
