Cone Formation in Sequoia Gigantea. I. The Relation of Stem Size and Tissue Development to Cone Formation. II. The History of the Seed Cone

Buchholz, J

The vegetative stem tips of Sequoia gigantea show a wide range of dimensional variation. The diameters of stems range from leaders of more than 4 mm. down to twigs less than 1.3 mm. The larger stems have proportionately larger steles and larger wood cylinders than small stems, such that the diameters of the steles and wood cylinders increase more rapidly than the total stem diameters. This relationship may be graphically represented by the slope of a line resulting from the logarithmic plotting of the diameters of the stelar and wood cylinders against the total diameters of the stems. For the steles (including pith) and wood cylinders this slope representing the constant of relative size (k) is very nearly the same throughout the size range, but for the pith it differs in small stems. The reproductive stems have a slightly different formula, giving larger steles and smaller pith than vegetative twigs of corresponding diameters. These differences in stem tips are inherent in differences in the primary meristems, both for the vegetative stems of all sizes and for the reproductive stems. The cones of Sequoia gigantea are formed on the ends of reproductive stems in the season previous to pollination. The female cones are borne on stems in near relation to leaders. Their mean diameter (dry) is 2.54 mm., and the male cones are borne on stems 1.46 mm. in diameter. The female cones enlarge to full size in the season of their pollination, and though fertilization occurs in August of the same season, the seeds are not mature morphologically until the end of the subsequent season. Thus at least three years are included in the history of a seed cone. Mature cones are persistent and retain their seeds for many years after maturity of the embryos. During this period they remain green and appear to be active in photosynthesis. Their age may be determined by several methods, including the growth rings found in the peduncles of the cones themselves. Cones in excess of twenty years have been found. This feature of retaining the seeds in the cones with continued growth of their peduncles is one which not only distinguishes the big tree from the related redwood but is a unique feature among conifers.

Cone Formation in Sequoia Gigantea. I. The Relation of Stem Size and Tissue Development to Cone Formation. II. The History of the Seed Cone

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