Key message A technique whereby whole mounts of delicate tissues of differentiating xylem are imaged directly by polishing and block-face imaging of embedded microcores. Autofluorescence and image analysis aids identifying the stages of xylogenesis. Stem microcores from fast-growing trees, such as Pinus radiata (D. Don) with wide zones of cambium and differentiating xylem and very wide growth rings, pose a challenge for microscopy, as they are difficult to handle and easily damaged compared to slower growing species. A novel procedure has been developed which captures high-resolution images directly from the block face of large samples embedded in plastic resin without the need for sectioning or staining. Microcores of differentiating xylem of P. radiata growing in the central North Island of New Zealand were embedded in a low viscosity acrylic resin. The surface of the entire resin block was abraded and polished to expose cross sections of the wide zone of wood formation in these fast-growing trees without damage or distortion. Autofluorescence imaging was performed using a confocal laser scanning microscope. This avoided the need for staining and allowed the determination of the beginning of lignification based on lignin autofluorescence. Image analysis was used to determine the widths of: (a) the cambium, cell expansion, and wall-thickening zone (CET) and (b) the wall lignification zone (LT). A fast-growing tree had wider CET and LT zones than a slow-growing tree. This was due to the fast-growing tree producing more tracheids than the slow-growing tree, rather than by the production of larger tracheids.