8 THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 



hypothesis, that all angiosperms are hybrids, at least on the 

 maternal side? 



Numerous special arguments could be adduced. It may suffice, 

 however, to point out the genus Carex, in some of the best species 

 of which the pollen is in the same condition, three of the grains of 

 each tetrad being sterile and only one fertile. 1 ) Every single grain 

 of the ripe pollen is a tetrad, showing the very reduced rudimentary 

 remnants of three of its cells as a flattened investment of the 

 fertile one. 



In the article just quoted no parallelism has been attempted 

 between the presence of sterile pollen grains and the already nu- 

 merous 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. 2 ) 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 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 0. Lamarckiana and 0. 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 Geerts. 3 ) He sums up his results 



i) Juel, H. O., Die Entwickelung der Pollenkorner bei Carex. Jahrb. 

 Wiss. Bot. 35:649 — 656, 1900. 



2) Solms-Laubach, H., Capselia Heegeri Solms, eine neu entstandene 

 Form der deutschen Flora. Bot. Zeit. 10:167 — 190, pi. 7, 1900. 



Blaringhem, L., Fleurs proliferes du Cardamine des pr6s. Bull. Soc. 

 Bot. France 60:304—311, 1913; and Les transformations brusques des 

 etres vivants. Bibl. Phil. Sci. Paris 191 1 (see pp. 119— 147). 



3) Geerts, J. M., Beitrage zur Kenntnis der Cytologic und der par- 



