Maturation of Ray Parenchyma Cells in Pine

In the ray parenchyma of hard pines, development of pitted walls and lignification is generally delayed. Maturation appears to take place gradually with aging of the sapwood in the hard pines with fenestriform pits, and somewhat more abruptly as the sapwood-heartwood boundary is approached in the hard pines having pinoid pits. When lignification begins in hard pines, it generally commences at the corners of those ray parenchyma cells contiguous to ray tracheids. Occasionally, isolated lignified elements can be found completely surrounded by as yet immature, unlignified tissue. Unlignified ray parenchyma cells can also be detected in heartwood, where presumably they would remain immature. The pattern of localized lignification suggests that the individual cell contributes significantly to the process of lignification. Wall thickening and lignification of ray parenchyma cells in coniferous genera other than the hard pines showed no indication of lagging behind other xylary elements. Unlike the hard pines, these other species exhibited cytoplasm, nuclei, and starch granules in lignified ray parenchyma cells. The apparent lack of lignification in many ray parenchyma cells in the sapwood of hard pines is contrary to other species either tested in this study or reported by other workers.

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