CHAP. I. INTRODUCTORY REMARKS. 5 



for cross-fertilisation are perhaps more obvious in the 

 Orchideae than in any other group of plants, but it is 

 an error to speak of them, as some authors have done, 

 as an exceptional case. The lever-like action of the 

 stamens of Salvia (described by Hildebrand, Dr. W. 

 Ogle, and others), by which the anthers are depressed 

 and rubbed on the backs of bees, shows as perfect a 

 structure as can be found in any orchid. Papilion- 

 aceous flowers, as described by various authors for 

 instance, by Mr. T. H. Farrer offer innumerable 

 curious adaptations for cross-fertilisation. The case of 

 Posoqueria fragrans (one of the Rubiaceae), is as won- 

 derful as that of the most wonderful orchid. The 

 stamens, according to Fritz Miiller,* are irritable, so 

 that as soon as a moth visits a flower, the anthers ex- 

 plode and cover the insect with pollen ; one of the 

 filaments which is broader than the others then moves 

 and closes the flower for about twelve hours, after 

 which time it resumes its original position. Thus the 

 stigma cannot be fertilised by pollen from the same 

 flower, but only by that brought by a moth from some 

 other flower. Endless other beautiful contrivances for 

 this same purpose could be specified. 



Long before I had attended to the fertilisation of 

 flowers, a remarkable book appeared in 1793 in Ger- 

 many, 'Das Entdeckte Geheimniss der Natur,' by 

 C. K. Sprengel, in which he clearly proved by innumer- 

 able observations, ho.w essential a part insects play in 

 the fertilisation of many plants. But he was in ad- 

 vance of his age, and his discoveries were for a long 

 time neglected. Since the appearance of my book on 

 Orchids, many excellent works on the fertilisation of 

 flowers, such as those by Hildebrand, Delpino, Axell, 



'* 'Botanische Zeitung,' I860, p. 129. 



