60 



When the black sort Moss (0670) which, as we have seen, apparently 

 possessed a unit for Grey as well as a unit for Black, was crossed with the 

 yellow sort Gold Rain (0386) there were obtained in the second generation, 

 Blacks, Yellows, Greys and Whites, the two latter representing apparently quite 

 new forms (49, p. 48). The proportions of the different forms of hybrids 

 obtained showed furthermore, that the crossing had been a trihybrid one that 

 is, three character pairs had been involved. These may be represented in the 

 following scheme : 



Gold Rain 



b (absence of black) 

 g (absence of grey) 

 Y (Yellow) 



The gametes (sexual cells) formed in this case are of eight kinds, viz. : 

 BGY,BGy,BgY,bGY,Bgy,bGY,bgY,bgy. 



In the second generation the progeny of four individual plants from F l 

 were grown in separate cultures and gave the following results : 



(a) F 2 116 Black, 22 Grey, 5 yellow-yellowish, 2 Grey and yellow, 10 White. 



(b) " 54 " 11 " 9 2 "3 " 



(c) ." 29 " 6 " 3 " 4 



(d) " 59 " 14 "3 " 1 " " 5 " 



Total 258 " 53 " 20 " 5 " 22 " 



The second theory, or modification of the Mendelian theory, to which 

 The theory reference has already been made as seeming to contribute to a better under- 

 that certain s t anc [ m g o f the origin of hereditary gradations and to the occurrence of 

 may possess aberrant types, has been advanced by Nilsson-Ehle (46 and 49) in connec- 

 more than one tion with work with cereal grains, and by East (11) of the United States of 

 unit, each of America, with Maize. This theory assumes that a certain character may con- 

 which has the s i s t O f more than one unit, each unit having practically the same external effect, 

 same external ^ UQ ft nas j^ o b serve( j that a black-kernelled oat sort may possess more 

 effect 



than one unit for Black, each unit alone being able to produce the typical 



black colour. A good example is afforded in the crossing between the black 

 sort 0668 and Ligowo, 0353 (white). The former sort has been found on 

 analysis to contain two independent units for Black (B^ B 2 ) and also a unit 

 for Grey (G) , all of which are apparently absent in the sort 0353. The con- 

 stitution of these sorts is represented in the following manner: 



0668, B, B 2 G. 

 0353, b t b 2 g. 



This crossing is therefore a trihybrid one instead of the simple mono- 

 hybrid, although the latter might reasonably be expected in the absence of 

 any exact knowledge as to the inner constitution of the sorts involved. 



