Cheeseman.— On the Fertilisation of Acianthus and Cyrtostilis. 351 



estimated that about one quarter of the flowers produce capsules ; but from 

 subsequent observations I am now convinced that the number is much less. 

 Corysanthes offers a case of imperfect fertilisation even more singular. In all 

 the species the proportion of capsules produced is very small, and large 

 patches can often be found that have failed to mature a single one. As an 

 illustration, a bed of Corysanthes triloba, in a favourable situation for the 

 visits of insects, expanded, during the last season, over two hundred flowers : 

 yet of this large number only five succeeded in ripening capsules. We must 

 be cautious, though, in assuming that the imperfect fertilisation of these plants 

 is of much real disadvantage to them. In mafiy districts Pterostylis truUifolid 

 is quite as abundant as Acianthus ; while the less general distribution of the 

 species of Corysanthes is probably due to their organization not being so well 

 adapted to a variety of conditions and habitats, rather than to the scarcity of 

 seed produced. In their special localities they are often abundant. 



2. Cyrtostylis oblonga. 



The great resemblance that this plant bears to Acianthus, induced me to 

 suppose that its fertilisation would be conducted on the same plan, and this 

 appears to be the case. We find in Cyrtostylis, as in Acianthus, the lip 

 horizontally spread out, secreting abundance of nectar ; the column arching 

 over it ; the points of the rostellum hanging downwards, with the pollinia 



firmly fastened to their upper margins ; together with other contrivances, all 

 apparently co-ordinated, so that an insect, having once entered the flower, can 

 hardly avoid attaching itself to the pollen- masses, and removing them on its 

 departure. 



On comparing the flowers of the two plants, we at once find a difference 

 in the structure of the lip. In Acianthus this organ is concave, for the 

 purpose of storing up nectar to serve as an attraction for insects : in Cyrtostylis 

 it is narrow, and quite plain ; but the same end is attained by allowing the 

 nectar slowly to trickle down each side of the midrib. The secreting glands 

 at the base of the lip are much smaller than in the former species, while the 

 papillae on the margins and points are totally wanting. The column agrees 

 with that of Acianthus in most features, but is broadly winged on each side. 

 This may be of use as a protection to the stigma, or perhaps the projections 

 serve as guides for the proper withdrawal and insertion of the pollen-masses, 

 No difference worth mention is found in the stigma, or rostellum ; and the 

 mode of attachment of the pollinia to the latter organ appears to be precisely 

 the same in both plants. In the shape of the pollen-masses themselves, 

 however, we find a marked divergence, for instead of being nearly subdivided, 

 as in Acianthus, they are simply falcate in shape. They are laterally much 

 compressed, and extremely friable. 



