48 THIRD REPORT — ISoJ. 



ferences whatever in texture between tliat part and the general 

 surface of the stigma" (meaning what I have described as the 

 discoid head of the style) : but this is not the place for entering 

 into the discussion of these subordinate points. 



Orchidece are another tribe in which similar difficulties have 

 been found in reconciling structure with the necessity of con- 

 tact between the pollen and stigma in order to effect impregna- 

 tion. Indeed it seems in these plants as if every possible pre- 

 caution had been taken by nature to prevent such contact. 

 Nevertheless it is represented by M. Adolphe Brongniart, in a 

 paper read before the Academy of Sciences of Paris in July 

 1831 *, that contact is as necessary in these plants as in others, 

 and that in the emission of pollen-tubes they do not differ from 

 other plants. These statements have been followed up by Dr. 

 Brown f, in itn elaborate Essay upon the subject, in which the 

 results that are arrived at by our learned countryman are es- 

 sentially to the same effect. To these tliere is at present no- 

 thing equally positive to oppose ; but as the indirect observa- 

 tions of Mr. Bauer %, and the general structure of the order, are 

 very much at variance with the probability of actual contact 

 being necessary, and especially as Dr. Brown is obliged to have 

 recourse to the supposition that tlie pollen of many of these 

 plants must be actually carried by insects from the boxes in 

 which it is naturally locked up, — it must be considered, I think, 

 that the mode of fertilization in Orchidece is still far from being 

 determined. I must particularly remark that the very proble- 

 matical agency of insects, to m hich Dr. Brown has recourse in 

 order to make out his case, seems to be singvilarly at variance 

 with his supposition § that the insect forms, which in Oplirys 

 are so striking, and which he finds resemble the msects of the 

 countries in which the plants are found, are intended rather to 

 repel than i^^ attract. It may be true, as Dr. Brown observes, 

 that there is less necessity for the agency of insects in such 

 flowers as the European OpJinjdecs ; but what other means 

 than the assistance of insects can be supposed to extricate the 

 pollen from the cells in the insect flowers of such plants as 

 ReiioufJiera Arac/iniies, the whole genus Oncidiian, Teiramicra 

 rigldn, several species of Epidendrinn, Cipnbidlum tenuijolium, 

 Vanda peduncidans, and a host of others ? 



* Annales des Sciences, vol. xxiv. p. 113. 



t Observations upon the Organs and Mode of Fecundation of Orcliidese and 

 Asclepiadese. 



X Illustrations of the Genera and Species of Orchideovs Plants. Part II. 

 " Fructification," tabb. 5. 12. 13. ] k 



§ " Proceedings of tlie Linnean Society," June o, 1832, as given in the Lon- 

 don and Edinburgh Philosopliical iMagcuiitc and Journal. 



