ipisl DE VRIES— OENOTHERA BIENNIS 191 



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 shghtly 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 

 for years. It is not an uncommon case that the proportion of the 

 rapidly germinating seeds is a very small one, and in this case 

 a large quantity of seed is necessary to secure a small number of 

 seedlings. Moreover, in those cases where the seeds do not pro- 

 duce a uniform progeny, but a mixture, as, for example, with twin 

 hybrids or in hybrid splitting, the possibility cannot be denied that 

 the numerical proportion of the components of the mixture may 

 be different for the rapidly germinating seeds as compared with 

 the others. In other words, percentage figures may be influenced 

 to some degree by the occurrence of a more or less, considerable 

 proportion of dormant seeds. 



In order to ascertain the value of this objection, I have made 

 from time to time cultures in which the rapidly germinated seed- 

 lings were planted out separately from the slower ones. As a 



