Aug. 6, 1917 Studies on Oat Breeding 295 



toward the base of the panicle. Along with the reduction of the length 

 of the pedicels, there occurs also a reduction of the number of flowers 

 or kernels within the individual spikelets from the top of the main axis 

 toward the base of the panicle. The same is true, but to a less extent, 

 for each whorl. The tip spikelets of a given whorl are always the longest 

 spikelets, and contain more flowers than any other spikelets in that 

 whorl. Near the base of each whorl the spikelets show a marked reduc- 

 tion both in length and in number of flowers. This reduction of the 

 number of kernels in the spikelets at the base of the whorl and of the 

 panicle in conjunction with the shortening of the pedicels gives the 

 spikelets in those regions of the head almost the appearance of those 

 on a common hulled oat. 



The reduction in the size and number of the spikelets which takes 

 place gradually from the top to the base of the panicle and of each whorl 

 recalls the well-known fact that the heaviest kernels in the oat panicle 

 are borne near the top of the head and at the tips of the whorls. The 

 lightest kernels are found at the base of the whorls and of the panicle, 

 where sterility of the flowers quite often occurs. It is probable that the 

 same physiological causes that favor the development of the grain in the 

 uppermost regions of the common oat head account also for the larger 

 number of flowers or kernels and for the greater length of the pedicels in 

 the uppermost spikelets of the naked oat. 



Another interesting feature of the spikelets of the naked oat is pre- 

 sented by the nature of the glumes. A multiflorous spikelet of the naked 

 oat used in this cross bears at its base a pair of yellowish outer empty 

 glumes, the glumse proper, which cover the flowering glumes, or rather the 

 palese. The lower flowering glume, or the palea inferior, is slightly longer 

 than the corresponding outer sterile glume. The upper, inner glume, the 

 palea superior, however, is much shorter, reaching only to about the 

 middle of the palea inferior (Pi. 41,5). The length of the lower and upper 

 flowering glume averages about 22.7 and 13.3 mm., respectively. This 

 proportion between the size of the lower and upper flowering glume, 

 characteristic of this naked oat, obtains also in the remaining flowers of 

 the multiflorous spikelet. The outer flowering glume sometimes bears 

 a very weak, straight awn. Whenever the awns are present, they are 

 borne chiefly by the spikelets on the lower whorls. The rare occurrence 

 and weak nature of the awns suggest that the strain used in this cross 

 belongs to the variety Avena nuda var. inermis. 



The structure of the lower flowering glume is very characteristic of the 

 naked oat. As pointed out in another paper by one of the present 

 writers (12), the lower flowering glume of the common oat represents a 

 very strong protective organ of the flower and fruit of the Gramineae, 

 being composed of four layers of cells, two layers of which, thickened and 

 reenforced by a deposition of silicious matter and silicious cells, represent 



