Thickness of upper and lower epidermis of leaves , width of xylem and phloem of annual and biennial branches , ratio of late wood to early wood , periderm thickness of biennial branches , and length of xylem ray present decreasing trends with latitude ascending ; while ratio of palisade tissue to spongy tissue , epidermis thickness of annual branches , and cortex thickness of biennial branches show unobvious variations with latitude increasing 葉的上下表皮厚度、 1和2年生枝木質(zhì)部及韌皮部寬度、晚材早材比值、 2年生枝的周皮厚度、木射線長(zhǎng)等均隨緯度升高而呈下降趨勢(shì);而葉的柵欄組織和海綿組織比值、 1年生枝表皮厚度、 2年生皮層厚度等解剖結(jié)構(gòu)隨緯度變化沒有明顯規(guī)律。