Colour Forms of Ottawa District Orchids 
Allan H. Reddoch and Joyce M. Reddoch 
Colour in Flowers 
Human beings throughout much of the world and much of 
history have admired the beauty of flowers, their form, their 
fragrance and their colour. Why this should be so seems puzzl¬ 
ing, for there is little to be gained in comparison, say, to 
admiring fruit that may lead to a nutritious meal. Certainly, 
there would have been little evolutionary advantage to the plant 
to attract humans who would pick the flower. 
The basic function of flowers is to exchange pollen with 
flowers on other plants for the production of seed. Some 
plants, including grasses, most of our trees, and ragweed, 
simply allow the wind to blow the pollen from one plant to 
another. Much of it, as every hayfever sufferer knows, does not 
reach its target. In such plants, the flowers are usually 
small, green and inconspicuous. Other species, however, seek a 
more efficient transfer and enlist the aid of insects or birds 
to carry the pollen from plant to plant. To do so, these plants 
need to advertise with showy flowers and to provide some induce¬ 
ment in the form of nutritious nectar. Admittedly, there is 
some deceptive advertising by some species where the flowers are 
showy but no nectar is provided. To improve the efficiency 
still more, some species, particularly orchids, have developed 
very cunning techniques to ensure that suitable insect visitors 
are, in effect, forced to carry pollen, and to do so in such a 
way that the pollen is properly deposited on the next plant. 
The flower colour (and sometimes odour) must attract a 
suitable pollinator and be sufficiently characteristic that the 
pollinator can then find another plant of the same species. The 
flower may then have those colours that an appropriate pollina¬ 
tor can see: yellow and blue as well as ultraviolet for bees; 
reds for birds; reds and purples for butterflies; and pale 
colours and white for night-flying moths. 
The colours are produced by a small number of classes of 
pigments: anthocyanins, which tend to be red, pink, blue or 
purple; carotenoids, which are yellow or orange; and chloro¬ 
phyll, which is green. The production of these pigments is 
determined genetically, and it is clearly advantageous to main¬ 
tain reasonable uniformity of colour to ensure user loyalty, as 
well as uniformity of flower shape to ensure efficiency. 
* Part II in a series on Ottawa District orchids; Part I ap¬ 
peared in the last issue. 
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