FERTILISATION. 



75 



To make a slight digression — It may be here stated that the 

 duration of some orchid floAvers is very remarkable ; GrammafojiJii/J/Hiii 

 inulfifloruiii retains its flowers with scarcely any perceptible change of 

 colour for nearly one-third of the year ; the flowers of some of the 

 recently introduced Dendrol)es ^vith elongated spathnlate petals (D. 

 Strat!ot('s, D. Sfrehloceras), to wliicli may be added D. Dearei and a 

 few other eastern ^lalavsian species, c(nitinuc in peifection for upwards 

 of three months ; many Cypripedes persist from six to eight weeks 

 according to the season of the year, Avliile the leathery flowers of 

 some Vandas, Cymbidinms, and of other genera last nearly as long ; 

 the wax-like flowers of Aerides and Saccolabium generally retain their 

 beauty from three to four weeks ; and in the cooler atmosphere of 

 the Odontoglossum house the Odontoglots, Oncids and brilliant 

 Masdevallias lose none of their gorgeous tints for as long a period. 

 The duration of orchid flowers, apart from the absence of any fertilising 

 agent is, however, influenced by the texture of their perianth segments ; 

 the delicate sepals and petals of the labiate Cattleyas, Thunia, Sobralia, 

 Pleione, some of the Phalaenopses, etc., succumb to the damp and heat 

 of their environment sooner than those endowed with firmer texture. 

 But whether the duration of the flowers be longer or shorter, the 

 essential cause is the same, and this we now proceed to consider. 

 The evidence of the incapacity of most orchid flowers for self- 

 fertilisation afforded by the common observation of their failure to 

 do so under the artificial circumstances in which they are placed 

 in this country, is rendered conclusive by an examination of their 

 structure and of the various contrivances by which their fertilisation 

 is effected. These contrivances, as Mr. Darwin has most eloquently 

 and distinctly proved^ " are as varied and almost as perfect as many 

 of the most beautiful adaptations in the animal kingdom,"* but they 

 have for their main object not the fertilisation of each flower by 

 its own, but by the pollen of another flower. The agency by 

 which this is effected is provided by the Insect World, and it 

 has been abundantly demonstrated from direct observation that the 

 flowers of the greater number of species of our native orchids are 

 fertilised by the insects visiting them, and the process by which 

 this is accomplished has been accurately described not only by 

 Mr. Darwin but also by others who have followed in his footsteps. f 



* Fertilisation of Orchids, p. 1. 



t The eailiest observer of tlie fertilisation of on^hid flowers by insects was Cliristopher 

 Konrad Sprenf^el. This remarkable man, the son of a clergyman, was born at Brandenburg 

 in 1750. From 1774 to 1780 he was employed as a teacher in Berlin when he obtained 

 the appointment of Head Master of the school at Spandau. During his residence at 



