Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/193

. VI. Fritz Müller, the ovules of many endemic Epidendreæ and Vandeæ in Brazil remain in a very imperfect state of development for some months, and even in one case for half a year, after the flowers had been fertilised. He suggests that a plant which produces hundreds of thousands of ovules, would waste much power if these were formed and did not happen to be fertilised, and we know that fertilisation is a doubtful and difficult operation with many Orchids. It would therefore be an advantage to such plants, if the ovules were not at all developed until their fertilisation was assured by the pollen-tubes having already penetrated the stigma.

Coryanthes.—I will conclude this chapter by giving an account of the fertilisation of the flowers of Coryanthes, which is effected in a manner that might perhaps have been inferred from their structure, but would have appeared utterly incredible had it not been repeatedly witnessed by a careful observer, namely, the late Dr. Crüger, Director of the Botanical Gardens at Trinidad. The flowers are very large and hang downwards. The distal portion of the labellum (L) in the following woodcut, fig. 27, is converted into a large bucket (B). Two appendages (H), arising from the narrowed base of the labellum, stand directly over the bucket and secrete so much fluid that drops may be seen falling into it. This fluid is limpid and so slightly sweet that it does not deserve to be called nectar, though evidently of the same nature; nor does it serve to attract insects. M. Ménière estimates that the total quantity secreted by a single flower is about an English ounce. When the bucket is full the fluid overflows by the spout (P).