FLORAL COLOURS AND PIGMENTS. 



179 



Macfarlane notes the dull stone-white colour of the dorsal sepal of 

 Cypripedium Spicerianum, and explains it by saying that the inner 

 surface is copiously and uniformly beset with gland-tipped hairs, which in 

 all cases spring from colourless cells of the epidermis, but have some or all 

 of their cells often filled with a rich ruby pigment, the presence of which 

 in the hairs gives the dull stone colour to the sepal. 



The flower of Masdevallia Veitchiana owes its colour to the presence of 

 abundant orange chromoplastids in the epidermal and subjacent cells. In 

 the throat of the flower there are also abundant unicellular glandular hairs 

 full of purple cell-sap. The effect is peculiar and difficult to describe in 

 words. Were the purple anthocyan evenly spread in a thin sheet over the 

 orange xantheic pigment the result would certainly be a brown. As it is, 

 the colour effect is that due to the addition of some purple to orange 

 light, and not entirely to the absorption by orange pigment of the residue 

 from white light after passing through the purple pigment. 



In many Odontoglossums, Oncidiums, Tropceolum, and numerous 

 other flowers there is crimson anthocyan in the epidermal cells, and yellow 

 chromoplastids along the inner walls of the same cells as well as in the 

 subjacent cells. The colour effect is orange in such cases if the anthocyan 

 is in small quantity ; where it is plentiful the effect is brown, warmer or 

 colder according as the anthocyan is more inclined towards red or blue, 

 In Geum coccineum the anthocyan is very red, and the result is a bright 

 scarlet. 



In some Wallflowers the yellow chromoplastids are fairly evenly 

 distributed throughout the crimson sap of the epidermal cells instead of 

 lying along their inner walls, and the increased effect of the yellow is 

 evident in the floral colour. 



When the backing chromoplastids have a tinge of green, or when 

 chlorophyll corpuscles are present as in many Cypripediums, the colour 

 is a darker brown as in C. Boxallii, brownish-black as in C. insigne, or 

 almost quite black as in Cypripedium x Argus, for examples. 



In this connection mention may be made of the black blotches on the 

 leaves of Arum maculatum, and of the black stripes on the leaves of 

 Banunculus Ficaria, which are the result of crimson anthocyan overlying 

 green chlorophyll. 



In some forms of yellow Tulips the inner sides of the bases of 

 the perianth segments and the staminal filaments are green in colour 

 — in some places an evident green, in others a green so dark as to be 

 almost black. The colour is caused by blue anthocyan in epidermal 

 cells overlying yellow chromoplastids. Where the anthocyan is in small 

 quantity the green is bright and luminous ; where it is in very large 

 quantity the combined light absorption is almost complete. In the 

 upper portions of the same segments there are splashes of bright scarlet, 

 and here the overlying anthocyan is a brilliant red. On testing, it is 

 found that the epidermal cell-sap of the base of the segments is neutral 

 in reaction, whilst higher up it is strongly acid. 



When the outer sides of the bases of the flowers of Crocus aureus are 

 examined, green stripes are to be found there. The colour is due to the 

 combined effect of blue anthocyan in the epidermal cells of that side, and the 



