356 THE JOURNAL OF BOTANY 



Knospen oberhalb der Spitze der Antheren.* Wenn sich die 

 Bliithe offnet, breiten sich die vier Narben im Kreuz aus, dabei 

 die Antheren in der Kegel nicht beriihrend. Bei CE. biennis 

 dagegen liegen die Narben in der Knospe mitten zwischen den 

 Antheren und iiberragen diese zur Bluthezeit nicht. Dieser 

 Umstand ist fur die Befruchtung sehr wichtig. Bei CE. biennis 

 findet diese bereits in der Knospe statt, in dem die Antheren sich 

 einen Tag vor der Entfaltung der Krone offnen." 



The following table shows to what extent De Vries's definition 

 of CE. biennis can be relied upon : — 



Measurements of Flowers fully open of Oenothera biennis Linne 



(fide De Vries). 



Two specimens from the Botanic Garden of Amsterdam, received from 



Prof. De Vries, July, 1907. 



a. b. e. D. 



1. 27 14 14 26 



2. 27 9 13 26 



Thirty -five specimens from outside Spirit Building of Natural 

 History Museum, South Kensington, July-August, 1907. 





A. 



B. 



c. 



D. 



1. 



24 



11 



13 



24 



2. 



24 



10 



12 



24 



3. 



21 



10 



10 



21 



4. 



20 



12 



9 



22 



5. 



20 



9 



10 



27 



0. 



19 



18 



12 



19 



7. 



19 



11 



11 



21 



8. 



19 



9 



11 



20 



9. 



18 



10 



11 



21 



10. 



18 



10 



10 



23 



11. 



18 



9 



11 



23 



12. 



17 



12 



12 



21 



13. 



17 



10 



11 



22 



14. 



17 



9 



9 



22 



15. 



16 



10 



10 



23 



16. 



15 



9 



10 



22 



17. 



15 



9 



10 



19 



18. 



15 



9 



9 



18 



In a (E. Lamarckiana from St. Cast (further on, No. 10) I have noted 

 that, although the pistil is much longer than the stamens, the stigma does not 

 project beyond the petals in the bud on the point of opening. There are, 

 therefore, ex. * ptions in both " species." 



t The same criterion for the groupment of the " elementary species" is 

 adopted by MacDougal (Mutants and Hybrids, p. 52) :-— " The evening-primroses 

 of eastern North America, from which probably all of the forms cultivated in 

 Europe are derived, may be divided into two groups— a group including CE. 

 biennis, nmricata, and cruciata, in which the flowers are comparatively small, 

 and in which self-pollination is possible and frequent. The second group, 

 including species native to a region further south, comprises CE. argillacea, 

 (E. grandiflora, and (E. Lamarckiana, in which the flowers are large and the 

 stamens are much shorter than the pistil, a condition which with some accessory 

 structures favours cross-pollination." 



