Primrose Hybrids.— l^\\e.n the "Chinese" form \Pri7n- 

 ula sinensis) with wavy, crenate petals and the " Star " form 

 (P. stellata) with fiat, entire petals are crossed the hybrids or 

 Fi are intermediate in form. The Fo generation has 25% 

 Chinese, 25% Star and 50% intermediate forms. 



2 — Peaches and Nectarines 



Darwin many years ago showed that nectarines may 

 come from the seeds of peaches, that peaches may come 

 from the seeds of nectarines and that peach trees made by 

 bud sports produce nectarines. 



The explanation of these facts is now made clear since 

 Mendel's discoveries, if we assume, as we are correct in 

 doing, that the nectarine is a smooth variety of the peach, 

 and that this smoothness is recessive to the hoariness of the 

 peach. When, therefore, nectarines spring from the seeds 

 of peaches it is a case of a recessive form arising from a dom- 

 inant hybrid. When peaches are produced from the seeds 

 of nectarines it shows that the nectarine has been pollinated 

 from a peach. 



Crossing in Oats. — Surface made crosses of strains of 

 wild oat {Arena fatua) and Cultivated oat (A. sativa) to de- 

 determine the inheritance of the callus at the base of the 

 fertile floret. 



The Fi generation showed an intermediate form of 

 callus, but in subsequent generations typical Mendelian 

 segregation occurred. It was found, moreover, that the 

 presence or absence of awns and pubescence in the hybrids 

 was perfectly correlated with the condition of the callus as 

 in the original forms. 



Problem. — Determine the F,, Fo and F3 generations in 

 the case of crossing a wheat with a long lax 

 head with one having a short dense head. 



3 — Pin-eyed and Thrum-eyed Primroses 



Darwin called attention to the beautiful adaptation in 

 these dimorphic forms of Primrose to insure cross-fertiliza- 

 tion. Morgan {Evolution and Adaptation, p. 369) says: 

 " If these two forms should appear as mutations and if, as is 

 the case, they do not blend when crossed, but are equally 

 inherited, they would both continue to exist as we find them 

 to-day." 



Darwin also found a third, a large-eyed form with 

 short style and stamens low in the tube, which he termed 



98 



