Excerpt from Form-Factors in Coniferae

With the great development of the cone-scale growth in the Abietineae, often appearing in section as an outgrowth of the base of the massive inverted and fused ovule, new possibilities of wing-development are opened up, as the abscission-line of the fused ovule cuts a new path along the cone-scale surface to extend along the intercalated region as a secondary slip of 'wing' - material. From the preceding restriction of the ovules to 2 per scale, symmetrically placed, it follows that the area of the free cone-scale surface may be equally divided between the 2 seeds, giving each a unilateral wing, the length and breadth of which are controlled by the growth capacity of the cone-scale. An effective spinning wing is thus attained in a wholly secondary manner, which compares in efficiency with the spinning wing of any other fruits or seeds of Angiosperms; the efi'ect being intensified by the sclerosed texture of the tissue, as correlated with the weight and pointed apex of the seed. Length of wing, as giving the radius of the spinning circle, strength of the anterior margin, and weight of the seed, are important factors, resulting (pz'nus qveslrz's) in the attainmentof a limiting velocity of 2-4 to 3 ft. Per sec. After a drop of only 3 ft. Or so from the cone. Range for the seeds of the same tree may be considerable, according to variations in length and width of wing; average measurements suggest as normal Pz'nus excelsa, 3 ft. Per sec.; Pz'cea Morz'na'a, 2-9; Cedrus Lz'éanz', 2-7 P. Auslrz'aca, the general approximation of different genera being very close. With such a limiting velocity it is clear that, given air-currents deflected from the surface of the ground with a vertical component of 2 miles an hour, the seeds would not fall at all, but might be indefinitely drifted or whirled upwards. Such generalizations apply to other winged seeds and fruits of Angiosperms, but no case gives more efficient or more uniform results for the material and mechanism. It may be added that Cedrus, with wing broadened distally in correlation with the broad cone-scale lamina, presents no apparent advantage. Seeds without endosperm, being lighter, are less efiicient. The 2 seeds of one scale spin in opposite directions; the edge nearer the middle of the scale is anterior' in spinning.

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