MALADIE ET SYMBIOSE 281 



case of imperfect self -fertilisation. Apparently we have here 

 a low form of biological intercourse, the insects being very 

 insignificant as " partners." Quite likely, too, the carbo-hydrates 

 offered by these orchids are of little value, and the fungi have 

 already had the lion's share of what production there is. The 

 poverty of solid food production on the part of orchids generally, 

 seems a noteworthy fact, testifying to the inferior value of 

 Norm-Symbiosis in the case of these plants. 



Another member of the Arethusese, Pterostylis trullifolia also 

 fails to secrete nectar. The flowers seem to be frequented 

 exclusively by Diptera (flies) again a low intercourse " but," 

 says Darwin, " what attraction they present is not known, as 

 they do not secrete nectar." 



Of Vanilla aromatica, the flowers of which are adapted to be 

 fertilised by insects, Darwin says that when this plant is cultivated 

 in foreign countries, for instance in Bourbon, Tahiti, and the 

 East Indies, it fails to produce its aromatic pods unless artificially 

 fertilised. According to him, this shows that 



some insect in its American home is specially adapted for the work ; and 

 that the insects of the above-named tropical regions, where the Vanilla 

 nourishes, either do not visit the flowers, though they secrete an abun- 

 dance of nectar, or do not visit them in the proper manner. 



But if the production of the aroma, and what this entails in 

 physiological and biological advantages to both producer and 

 consumer, is thus evidently closely associated with fertilisation 

 best performed by animal agency this shows that productive- 

 ness generally follows in the wake of Norm-Symbiosis. Anything 

 which detracts from such Symbiosis, must lead to inferior adapta- 

 tions, to weakness, and to retrogression. 



Again, in another case, Darwin records that the nectar of a 

 Guatemala Orchid seemed too powerful for our British bee, for 

 it stretched out its legs and lay for a time as if dead on the 

 labellum, but afterwards recovered. 



We may conclude that it is not the production of nectar 

 per se which determines the value of Norm-Symbiosis, but that 

 it is the physiological condition, the origin, nurture, etc., of the 

 nectar which are the determining factors. And if this be so, it 

 follows that in carbo-hydrate as in scent production, any 

 interfering secondary cause, such as Luxury-Symbiosis, may easily 

 result in the deterioration of the product originally adequate 

 enough to Norm-Symbiosis. 



