A. St Clair Caporn 245 



The whole group showed a rough approximation to a ratio of 3 grey : 

 1 white, but among the pure tights the ratio was practically 2:1. If, 

 however, it were a case of partial coupling of tight paleae with white- 

 ness, a much greater bias in favour of greys than actually exists should 

 occur at the opposite end of the scale. 



Nothing similar was found among the pure tights in the Nubian 

 Black crosses carried on to the jPg generation this year. Segregations 

 in four families are shown in Table VII. All these are quite normal 



TABLE VIT. 

 Nuhischer schwarzer x A. nuda. 

 Pure tights only from F^ generations. 



segregations. The first conforms to the ratio 3:1, the second 60 : 3 : 1, 

 and the last two 15 : 1, the parent gametes producing the Fi plants 

 being as shown, where B and B' are factors for black, and G for grey 

 colour. This cumulative black in the Nubian parent will be discussed 

 in another paper. The point to note here is that the colour inherit- 

 ance is on ordinary lines and that no linkage of a particular colour 

 with tight paleae is manifested. The apparent indications, inconsistent 

 and irregular, of coupling seen in parts of Table VI must therefore be 

 ascribed to the weathering, damage by mice, and consequent experi- 

 mental error. For evea on the whole count the error is large. 



Summary. 



1. In "pure tight" varieties complete sclerosis of all the outer 

 paleae is found. The spikelets are from 2 to 4-flowered. 



2. In Avena nuda all, or most, of the paleae are membranous ; a 

 few tight grains may occur up to a proportion of over 40 °/^ ; but " pure 

 tight " forms are never thrown. 6 to 10-flowered spikelets are found. 



Journ. of Gen. vn 17 



