Interspecific comparison of hybridization intensities in secondary xylem. A-F: Pair-wise comparison of white spruce and six other species based on the number of shared positive probes indicated in the plots. The squared correlation coefficients (r2) are as follows 0.86 (A), 0.85 (B), 0.89 (C), 0.29 (D), 0.22 (E) and 0.27 (F). G: Analysis of signal intensity variation between species; the fold change (FC) was determined from the average normalized signal intensities (log2 scale). An FC of 1 or −1 represents a two-fold signal increase or decrease, respectively. For phelloderm results, see Additional file 4: Figure S3.