A. St Clair Caporn 231 



The parental stock used showed impurity if the "nuda" type be 

 taken as one in which the paleae are all absolutely membranous, that 

 is to say, with no trace whatever of intervascular sclerosis. For some 

 plants had at least one obviously tight grain, often more, the pro- 

 portion of tights even rising to 40 "/^ in extreme cases, while others 

 would have a grain or two with paleae moderately stiffened in a 

 broadened midrib region. 



One important character, however, is common to all these forms : 

 they never throvj offspring with all the grains tight. In this respect, 

 therefore, even if not in others also possibly concerned in the partial 

 tightening of the paleae, they may be regarded as constituting a pure 

 line. 



In colour the parent plants were mixed greys and whites. Greys 

 are very easily overlooked in Avena nuda because colour is developed 

 only on the small inner paleae. 



The ^1 Generation. 



Spikelets. 



The panicles of the F^ plants contained a varying proportion of 

 many-flowered spikelets of the " nuda " type. In the basal regions the 

 two-flowered spikelet predominated. 



Paleae. 



Every conceivable gradation from the "pure tight" of the tight 

 grained parents to the wholly membranous palea occurred. 



On rubbing out, it was noticed that sometimes there was an excess 

 of tight grains, and sometimes not. Six separate panicles, which all 

 threw the same range and similar proportions of F^ types, and must 

 therefore have been Fi heterozygotes of the same factorial composition, 

 were constituted as follows 



TABLE I. 



Avena nuda 9 x Thousand Dollar ^ . 



Panicle 1. Excess of loose grains. Tights about ^ of total 



j> 2. ,, ,, ,, ), •§• ,1 



„ 3. ,, tight ,, ,, i ,, 



Ligowo 9 X Avena nuda $ . 

 Panicle 4. Excess of tight grains. Tights about f of total 



)j &• )i »> >> >) 2 ' >> 



,, 6. ,, loose ,, ,, 1 ,, 



It was at first thought that the reason for this fluctuation might lie in 

 the fact that single panicles were examined instead of whole plants ; but 



16—2 



