THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L 21 



flowers, those of 0. biennis sulj urea x biennis show the same bright 

 yellow as the parent species. 1 ) 



On experimental germination of seeds. 



Of the seeds of Oenothera Lamarckiana ordinarily only about 

 one-third produce seedlings, and this proportion is highly variable, 

 depending mainly on the conditions of cultivation of the parent 

 plant. Among the remaining seeds some contain a normal embryo, 

 others a more or less completely decayed one, while still others 

 are empty. The last have been thoroughly studied by Renner, 

 who found that they have been fertilized as well as the normal 

 seeds and those with decayed embryos. Between these normal and 

 externally normal seeds are seen the numerous rudimentary ovules 

 which have not been fertilized, and have not essentially increased 

 their size after the fertilization of the others. These rudimentary 

 seeds have been described by Geerts, as referred to above. 



In the empty seeds the embryo develops only a little, just 

 enough to stimulate the seed coats to an almost normal develop- 

 ment, in size as well as in structure. For the most part these 

 empty seeds are a little smaller and especially a little less broad 

 than the others, and can therefore easily be picked out of a sample. 

 But quite a good many are externally exactly like good seeds 

 and cannot be distinguished from them without being opened. 

 Renner states that about one-half of the seeds are in this empty 

 condition. 



By means of a hard steel needle with a curved tip it is easy to 

 make the seeds burst, especially after a thorough wetting. The 

 seeds which contain a healthy embryo will discharge it; the 

 unhealthy seeds will protrude a slightly brownish pulp; and the 

 empty seeds show the lack of contents, except a thin layer of 

 endosperm in the embryo sack. The various groups may be counted 

 out in this way, but the limits between the originally empty seeds 

 and those which have become more or less empty by an early 

 decaying of their germs are not sharp and often dependent upon 

 the health conditions of the seed-bearing individual. 



Among the seeds with a normal and healthy embryo some will 

 germinate during the first days after sowing, especially if the 

 temperature is a favorable one. Others will follow sooner or later, 

 some after weeks or months, while still others may remain dormant 



i) Gruppenweise Artbildung, p. 298. 



