Sept. 1, 1920 Fixed Intermediate, Hordeum intermedium haxtoni 587 



with the 2 -factor hypothesis suggested. The stability of the homozygous 

 intermediate has been thoroughly tested. Some of these have been grown 

 since 191 2 under widely varying conditions with no indication of reverting 

 to either the 6-rowed or 2 -rowed parental type. Many hybrids have been 

 made with the intermedium form as one parent. There are complete rec- 

 ords of the progeny of crosses on five 6-rowed and on two 2-rowed forms. 

 No 2-rowed segregates appeared among the progeny of the 6-rowed X in- 

 termedium crosses, and no 6-rowed segregates appeared among the progeny 

 of the intermedium X 2-rowed crosses. Every hybrid studied so far indi- 

 cates that H. intermedium has a genetic rank equal to H. vulgare or H. 

 distichon. 



In field culture there is always variation in the amount of fertility 

 present in the lateral florets of the intermedium form. This is true even 

 on a single plant. The earlier, better-nourished spikes in some strains 

 may have as high as 90 per cent of the lateral florets fertile. The later 

 spikes of the same plant usually have a diminishing percentage, while the 

 last-appearing may have lateral florets which are entirely sterile. Such 

 variations, however, are the result of variation in nutrition, for their 

 progeny are uniformly intermedium in type. 



There are variations of another sort in the intermedium forms which 

 have more significance. Frequent mention has been made of the fact 

 that the fertility of the different classes may be expected to vary with the 

 parents used. From crosses showing more vigor in the lateral florets of 

 the segregates than those of the Manchuria X Svanhals, very vigorous 

 intermediates may be isolated. From those crosses which show less fer- 

 tility in the segregates, homozygous intermediates probably may be iso- 

 lated in which only occasional kernels may be produced. Instances may 

 be possible where a potential intermediate may exhibit no fertility what- 

 ever. 



The form atterhergii shown in Plate 106 is probably an infertile inter- 

 medium barley. This form is somewhat anomalous in the taxonomy of 

 barley. It has never been grown by the authors, but from the statements 

 of those who have grown it, it appears to have shown no fertility. The 

 illustration is a photograph of a spike presented to the United States 

 Department of Agriculture several years ago by Mr. E. S. Beaven. It 

 has greatly enlarged lateral florets which closely resemble those of spikes 

 of H . intermedium, in which potentially fertile lateral florets are sterile 

 because of environment. 



REGRESSIVE 6-ROWED FORM 



The recognition of the two different forms homozygous for the 6-rowed 

 character offers a field for further investigation. The regressive 6-rowed 

 AAbb is apparently not optically distinguishable from the AABB 6-rowed. 

 There is no method known to the authors of separating these by inspec- 

 tion. In hybrids the regressive 6-rowed form should behave quite 



