266 SECRETION OF NECTAE. Chap. IX. 



importance to Orcliids by attracting insects, which are 

 indispensable for the fertilisation of most of the species, 

 yet good reasons can be assigned for the belief* that 

 nectar was aboriginally an excretion for the sake of 

 getting rid of superfluous matter during the chemical 

 changes which go on in the tissues of plants, especially 

 W'hilst the sun shines. The bractese of some Orchids 

 have been observed f to secrete nectar, and this cannot 

 be of any use to them for their fertilisation. Fritz 

 Muller informs me that he has seen such secretion 

 from the bracteae of an Oncidium in its native Bra- 

 zilian home, as well as from the bractese and from the 

 outside of the upper sepal of a Notylia. Mr. Eodgers 

 has observed a similar and copious secretion from the 

 base of the flower-peduncles of Vanilla. The column 

 of Acropera and Grongora likewise secretes nectar, as 

 previously stated, but only after the flowers have been 

 impregnated, and when such secretion could be of no 

 use by attracting insects. It is in perfect accordance 

 with the scheme of nature, as worked out by natural 

 selection, that matter excreted to free the system from 

 superfluous or injurious substances should be utilised 

 for highly useful purposes. To give an example in 

 strong contrast with our present subject, the larvae of 

 certain beetles (Cassidae, &c.) use their own excrement 

 to make an umbrella-like protection for their tender 

 bodies. 



It may be remembered that evidence was given in 

 the first chapter proving that nectar is never found 

 within the spur-like nectaries of several species of 

 Orchis, but that various kinds of insects penetrate 



* This subject has been fully 1876, p. 402. 



dispussed in my work 'On the t Kurr, 'Ueber die Bedeutung 



Effects of Cross and Silffertilisa- der Nektarien,' 18i?8, ]). 28. 

 tion in the Vegetal ile K ugdom,' 



