EVENING PRIMROSES 



'TPHE publication of DeVries' "Mutation Theory'' gave con- 

 siderable prominence to the evening primrose family, for 

 it was with one member of this group that many of the results 

 detailed in the book were obtained. The commonest species 

 of eastern America {Oenothera biennis) is a familiar w^eed 

 along roadsides and in other waste grounds whose yellow 

 flowers open in the late afternoon and close the next morning. 

 There is great variation in the size of the flowers and one 

 form with flowers much larger than usual has been named 

 grandiflora. It is probably this form, or one closely resembling 

 it, that DeV ries found in Holland and used in his experiments 

 in the production of new varieties. This form grows naturally 

 in some of the Southern States and since it achieved prominence 

 in the plant world the seeds have been offered by ^orists. 



One of the interesting things about the common evening 

 primrose is the rapidity with which the flowers expand. The 

 whole act of opening may be witnessed in the course of two 

 or three minutes if one selects just the right time of day for 

 his observations. A few minutes before the flow^er uncloses, 

 the bud may be seen to expand until the pressure on the enclos- 

 ing sepals is sufficient to cause them tO' separate and snap back- 

 ward in the position they occupy when the flower is expanded. 

 This movement is usually sufficient to shake the petals open 

 but if not, the)^ at once spread out with a motion that is quit, 

 noticeable. Few people have ever seen a flower actually open 

 for in most cases the process is so slow that it requires very 

 careful watching to note any progress, but in this plant there is 

 no difficulty in seeing the whole process. 



