iQisl 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.^'* Its 

 pollen is devoid of sterile grains. Here we have a clear case of 

 partial sterility not being the cause of mutability. On Jeffrey'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 niutabiUty 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 0. Lamarckiana and 0. biennis than 

 in the other members of the group. 



The question of the partial sterihty of the Onagraceae has been 

 most thoroughly dealt with by Geerts.'^ 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 



"■• Solms-Laubach, H., Capsella Heegeri Solms, eine neu entstandene Form der 

 deutschen Flora. Bot. Zeit. 10:167-190. pi. 7. 1900. 



Blakinghem, L., Fleurs proliferes du Cardamine des pres. Bull. Soc. Bot. France 

 60:304-311. 1913; and Les transformations brusques des etres vivants. Bibl. Phil. 

 Sci. Paris. 1911 (see pp. 1 19-147). 



's Geerts, J. M., Beitrage zur Kenntnis der Cytologie und der partiellen Sterilitat 

 von Oenothera Lamarckiana, Amsterdam, pp. 114, mit 24 Tafeln. 1901; see p. 93. 



