Comparision of Populus trichocarpa genes on our array that is homologous to xylem-predominant genes from other studies. Normalized intensity values for IN3 (internode 3) plotted against IN9 (internode 9). Upper and low diagonal lines show two-fold change ratio intervals. (A) Comparison to postulated Arabidopsis core-xylem genes . (B) Comparison to xylem-predominant transcription factor genes .