CHAP. VI. FERTILISATION. 285 



has taken great precautions to prevent contact, by so placing 

 the anther that it is next to impossible for the pollen to touch 

 the stigma until the energy of the former is expended. 

 Nevertheless, it is represented by Adolphe Brongniart, in a 

 paper read before the Academy of Sciences at 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 

 fi-om other plants. These statements have been followed up 

 by Brown, in an elaborate essay upon the subject, in which 

 the results that are arrived at by our learned countryman are 

 essentially to the same effect. To these there is at present 

 nothing equally positive to oppose ; but, as the indirect observ- 

 ations of Mr. Bauer, and the general structure of the order, 

 are much at variance with the probability of actual contact 

 being necessary, and especially as Brown is obliged to have 

 recourse to the supposition that the 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 fertilisation in Orchideas is still far 

 from being determined. I must particularly remark that the 

 very problematical agency of insects, to which Brown has 

 recourse in order to make out his case, seems to be singularly 

 at variance with his supposition that the insect forms, which 

 in Ophrys are so striking, and which he says resemble the 

 insects of the countries in which the plants are found, " are 

 intended rather to repel than to attract." It may be true, as 

 Brown observes, that there is less necessity for the agency of 

 insects in such flowers as the European Ophrydeae ; but what 

 other means than the assistance of insects can be supposed to 

 extricate the pollen from the cells in the insect flowers of 

 Renanthera Arachnites, the whole genus Oncidium, Tetra- 

 micra rigida, several species of Epidendrum, Cymbidium 

 tenuifolium, Vanda peduncularis, and a host of others. Is it 

 not, moreover, possible that the pollen of Orchideous plants 

 mav partake so far of the common properties of that form of 

 matter as to be capable of emitting (imperfect ?) pollen tubes 

 when brought into contact with the necessary stimulus, al- 

 though it is not their general character so to do, and although 



