1915] DE VRIES—OENOTHERA BIENNIS 177 
In the article just quoted, no parallelism has been attempted 
between the presence of sterile pollen grains and the already numer- 
ous published instances of mutations outside of the group of the 
evening primroses. Let us take for instance Capsella Bursa- 
pastoris, which has produced C. Heegeri and C. Viguieri.4 Its 
pollen is devoid of sterile grains. Here we have a clear case of 
partial sterility not being the cause of mutability. On JErrRey’s 
principle we must acknowledge C. Bursa-pastoris as a good species 
of undoubted gametic purity, and therefore it is evident that even 
the purest species may be in a mutable condition. From this we 
infer that mutability in itself does not justify the supposition of 
a hybrid origin, and that attacks on the gametic purity of the 
evening primroses have no real support on this side of the question. 
I have cultivated both C. Heegeri and C. Viguieri in my experiment 
garden; the first of them has globular and the other four-winged 
capsules. Both are historically known to have arisen suddenly 
from the parent stock, and come true to seed. 
JEFFREY lays stress mainly on the fact that partially sterile 
pollen is a widespread phenomenon among the allies of the evening 
primroses. Whether it runs parallel to their mutability has not 
been investigated, and as a matter of fact it does not seem to be 
much more highly developed in O. Lamarckiana and O. biennis than 
in the other members of the group. 
The question of the partial sterility of the Onagraceae has been 
most thoroughly dealt with by GrEerts. He sums up his results 
as follows: The genera Jussieua, Zauschneria, Epilobium, Bois- 
duvallia, and Lopezia are wholly fertile; they show neither rudi- 
mentary ovules nor sterile pollen grains. Only in Epilobium and 
Boisduvallia some rare pollen tetrads may sometimes miscarry. 
In the genera Clarkia, Eucharidium, Godetia, and Gaura all the 
ovules are fertile, but among the pollen grains about 30 per cent 
* Sotms-Lausacu, H., Capsella Heegeri Solms, eine neu entstandene Form der 
deutschen Flora. Bot. Zeit. 10:167-190. pl. 7. 1900. 
Brarincuey, L., Fleurs proliféres du Caslonine des prés. Bull. Soc. Bot. France 
60:304-311. eA and Les transformations brusques des ives vivants. Bibl. Phil. 
Sci. Paris. rgrt (see pp. due 
** Geerts, J. M., Beitrage is d 
von Oenothera Lomarckiona, ‘Amsterdam. pp. 114, , mit : 24 | Tafeln. 1901; see P. 93. 
int Ce sisee 
