3o8 Journal of Agricultural Research voi.x.No.e 



the manifestation of the pubescence can be observed on the same pan- 

 icle, even on the same whorl, in an intermediate form. The top spike- 

 lets in this case are usually naked, no manifestation of the pubescence 

 being possible. In the succeeding spikelets the lower grain may be naked 

 and the upper intermediately or firmly hulled, the pubescence, if the gene 

 for it is present, appearing at the base of the upper grain. Eighty-one 

 plants presenting this condition were observed. In the spikelets located 

 still lower on the whorl or panicle the glume of the lower spikelets become 

 coarser, adheres more closely to the caryopsis, in which condition the 

 pubescence appears already on the lower grain and decreases on the upper; 

 finally, the firmly hulled normal condition of the lower grain causes the 

 complete disappearance of the pubescence on the upper grain. Thus, a 

 single panicle or even whorl presents gradual changes in the local mani- 

 festation of pubescence, following the changes in the type of hull. 



This fact, as well as the evidence obtained from other crosses between 

 the Victor line and common hulled-oat varieties in which no case of an 

 upper grain being pubescent was observed, make it evident that the devel- 

 opment of pubescence at the base of the upper grain in the progeny of the 

 present cross is caused by the naked or seminaked condition of the lower 

 grain. Obviously, this naked or seminaked condition of the lower grain 

 causes a disturbance in the normal manifestation of the pubescence, and 

 it seems as though the gene for pubescence, suppressed or restrained in its 

 appearance in the normal region, tends to manifest itself at the base of 

 the upper grain, this latter thus taking the part of the lower grain. 



The examination of plants relative to the presence and absence of pubes- 

 cence at the base of the upper grain does not indicate a simple Mendelian 

 behavior. There are 209 plants with pubescent upper grain and 416 

 plants with smooth upper grain. The expected numbers are, on a 3-to-i 

 ratio, 156 pubescent to 469 smooth, the difference between the observed 

 and expected numbers being 53. This difference is five times larger than 

 the standard deviation ( Vn p q = 10.8) and is probably beyond the range 

 of fluctuation of random sampling. 



I The development of pubescence at the base of the upper grain in this 

 cross is then plainly the result of the modifications caused by the naked 

 parent. The same cause also accounts for the abnormal behavior of the 

 81 plants which develop a pubescence at the base of the upper grain while 

 the lower grain is smooth. Already a casual inspection shows that, since 

 in all the 81 plants the lower grain is naked or seminaked, the expression 

 of the gene for pubescence is prevented. This is borne out by the fact 

 that when the lower grain is completely hulled, as in the last group of 

 Tabic VIII — thus giving full opportunity for developing the pubes- 

 cence — none of the upper grains are pubescent. No single case has been 

 recorded in the literature of an oat with a smooth lower grain and pubes- 

 cent upper grain. As already pointed out, only certain wild oats normally 

 develop a pubescence on the upper grain, but even here the development 



