PLANT HYBRIDIZATION BEFORE MENDEL 215 



a white-seeded by a grey-seeded variety, and the dominance of 

 seed-coat color not being evident until the following generation, 

 there would consequently be no xenia effect. 



It is surprising, however, that Focke should have so clearly 

 overlooked the actual facts in the Goss experiment. The Blue 

 Prussian variety employed as the seed-parent had seeds with deep 

 "blue" cotyledons, or what would evidently properly be called 

 dark green. The pollen parent had "yellowish-white" seeds (i.e., 

 cotyledons). As the result of the cross, Goss obtained three pods, 

 which contained, when ripe, instead of the "deep blue" seeds of 

 the maternal parent, yellowish-white seeds, like those of the pol- 

 len parent. There was thus a perfectly clear case of what is now 

 known as dominance, of the sort referred to by Focke as "xenia." 

 The case of Seton is somewhat similar. A grey-seeded pea (i.e., 

 with grey seed-coats) was crossed with the pollen of a "white- 

 seeded" variety. A pod with four seeds was produced, all of which 

 are stated to have been green. There thus appears, so far as can 

 be judged, to have taken place in the first generation a dominance 

 of green cotyledon color over its absence (white), instead of the 

 usually reported case of the dominance of yellow cotyledon color 

 over green. That such was the case appears from the fact that the 

 seeds of the following year were mingled blue and white in the 

 pods, "mixed indiscriminately and in undefined numbers." 



They were all completely either of one color, or of the other, 

 none of them having an intermediate tint. It is thus quite evident, 

 that dominance for "xenia") took place in the first generation, 

 followed by segregation in the second. Gartner's case should have 

 been noted of a cross of "Early Green Brockel" {Pisiun sativum 

 viride) with green cotyledons, with "White-flowered creeping pea" 

 (Pisum sativum nanum repens) with yellow seeds, in which a 

 pod with five seeds, all yellow, was produced as the result of the 

 cross. (Gartner, "Versuche und Beobachtungen," pp. 84-5.) 



There was thus here a clear case of" color dominance ("xenia") 

 in the cotyledons Which does not appear to have particularly 

 attracted Focke's attention. 



Focke was, until his death in October, 1922, a practising physi- 

 cian of the city of Bremen. His interest in all biological, and 

 especially in botanical questions, was considerable. He was like- 

 wise interested in philosophical problems, and was a vigorous 



