Abstract
The shoot apex of Alnus jorullensis comprises two well-defined tunica layers and a corpus, which gives rise to foliar primordial and to procambial strands maturing acropetally. The primary shoot shows a eustek within abundant perenchyma consisting of isodiametric cells. Three leaf traces and three leaf gaps are seen at each node. Secondary xylem is made up of abundant, poorly lignified fiber tracheids, with apotracheal wood parenchyma, uniseriate and scantily biseriate xylem rays and apparently mucilaginous secretory cells. Vessel clements range about a mean length of 710 µm and a mean width of 70 µm with end-wall angles averaging 24° 56'. Perforation plates are scalariform, ranging fron 9 to 26 bars (Av. 16.48). In the course of the first year's growth, side-wall pitting changes from the metaxylemic reticulate-scalariform to the secondary opposite, bordered pattern.
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