1915] BARTLETT—MUTATION IN OENOTHERA II5 
are infinitesimal that all 9 would be included among rr plants 
chosen at random. 
3. A tetrahybrid might give as many as 16 phaenotypes in the 
F,. All of these would have a greater frequency than 1:255 
except the pure recessive. We have seen that mut. nuwmmularia 
cannot have a greater frequency than 1:255, and have also seen 
that it is not a pure recessive, for in the next generation after it 
originates it gives rise to several distinct types. 
4. In the case of one F, progeny. (Lexington C-91, see table ITI) 
from a single mother plant, 1,539 seeds from 6 capsules gave 3 
specimens of mut. mummularia, whereas 337 seeds from one capsule 
gave 5. Such a result shows a frequency varying from 1:60 
to 1:513 on capsules from the same spike. From a Mendelian 
standpoint it is practically impossible to explain such a result. 
The mutation phenomenon in O. pratincola cannot be explained 
away by any reasonably plausible stretching of Mendelian theory. 
On the contrary, it seems obvious that mutation is quite a different 
process from hybrid segregation, although both processes may 
occur simultaneously. 
Mut. nummularia is the only one of the mutations of O. pratin- 
cola the frequency of which has been determined. None of the 
others has been observed throughout the complete cycle from seed 
to seed and carried into a second generation. In tables II—XT all of 
the variants except mut. nummularia are thrown together as 
“other mutations or suspected mutations.” In explanation of this 
mixed category, it is necessary to state that all unusually small or 
unusually large plants, regardless of whether or not they appeared 
Otherwise different from the mass of the culture, were counted as 
“suspected mutations,” in order to be sure that no such variation 
as a mut. nanella would be passed over. To judge from past 
experience, most of the “suspected mutations” will develop as 
quite normal plants. Consequently the mutability of O. pratincola 
is probably not as great as might be assumed from the tables. 
Mut. Mummularia a discontinuous variation 
Critics of Dr Vries’ work on mutation in Oenothera Lamarckiana 
have not infrequently expressed skepticism as to whether or not the 
