Memoirs of the New York Botanical Garden, vol II, pp. 10-102 (1903)
The Influence of Light and Darkness upon Growth and Development
Daniel Trembly MacDougal, PhD

Cypripedium montanum Dougl.

Dormant specimens of Cypripedium were placed in the dark chamber in January, 1900, and began growth a month later. Two months later a young flower bud was pushed out from among the etiolated leaves, but did not open or attain normal size.

FIG. 56. A, epidermis from normal leaf of Cypripedium montanum. B, glandular hair from surface of normal leaf. C, epidermis of etiolated leaf. D, glandular hair from etiolated leaf.

The main stem attained a length of only 2 cm., which is only a fraction of that of the normal. The excessively elongated leaves were 15 cm. in length, and 2.5 cm. wide, while the normal leaves are 8 by 3.2 cm.

Epidermal cells from the lower surfaces of the etiolated leaves measured 32 by 4 while those of the normal were only 15 by 10. Etiolated leaves bore glandular hairs only, the pointed trichomes being absent. The shaft of the glandular hairs in the normal, consists of two cells with an average total length of 50 and diameter of 4, while in the etiolated the shaft was composed of four cells of an average total length of 110 with a diameter of 12. The apical gland measured 22 by 19.5 in the etiolated, and 16 by 13 in the normal.

From the above facts it is to be seen that the growth of Cypripedium in darkness is characterized by a non-development of the pointed hairs on the leaves, and the excessive development of the glandular trichomes. The first result is in accord with Schober's results, but no reason is at hand to account for the excessive enlargement of the glands and the multiplication of the cells in the stalk, unless these organs might be considered as aids to transpiration. The stomata of the leaves were of normal size, but of slightly attenuated outline, being apparently functionally normal.

The laminae maintained an erect position, and were more or less rolled during all of the period of their existence, embracing about a month.