172 BOTANY OF CROP PLANTS 



the base of the style, on the posterior side." This is probably 

 the "stylar canal" described by Poindexter. 



The outer and inner integuments vary in thickness from 

 two to four layers. The very large embryo sac is located at 

 the base of the nucellus. 



After fertilization, the following changes take place in the 

 maturing grain: 



1 . Outer integument disappears. 



2. Cells of inner integument become flattened, due to 

 pressure from within. 



3 . The middle and inner cells of pericarp become compacted. 



4. Cells of nucellus disappear to a large extent. 



5. Hardening of the cell walls of the pericarp. 



6. Fusion of pericarp and inner integument. 



Xenia in Com. — Xenia is the term appUed to the phe- 

 nomenon in which some character of the male appears at 

 once in the seed. For example, in crossing a strain of corn 

 having yellow endosperm with a strain having white endo- 

 sperm, the grains produced are all yellow in every case, no 

 matter which is used as the male parent. Xenia is shown 

 only in case the parent having yellow endosperm is used as 

 the male parent. The yellow endosperm character is 

 dominant over white endosperm. Pollen from the plant 

 bearing yellow endosperm will carry this character; pollen 

 from the plant bearing white endosperm will carry the white 

 character. When pollen, bearing the yellow endosperm 

 character, is placed on the stigma of the grain having white 

 endosperm, the pollen tube will discharge into the ovule two 

 male nuclei, each bearing the character for yellow endosperm. 

 One sperm nucleus fuses with the egg nucleus, the other 

 sperm nucleus fuses with the two polar nuclei. The result 

 of this triple fusion (second sperm nucleus and two polar 

 nuclei) is the endosperm. Now, since yellow is dominant. 



