Cheeseman. — On the Fertilization of the N.Z. Pterostylis. 355 



On several occasions I have artificially inclosed small insects in the flower. 

 Most escaped by crawling up the column and passing between the appendages, 

 and some, but not all, carried pollen-masses away with them. It can hardly 

 be expected, however, that insects selected at random would remove the 

 pollinia with the same ease and certainty as the species to whose requirements 

 the flower has no doubt been profoundly modified by natural selection, acting 

 during long periods of time. 



Although I have often watched the flowers I have never seen insects 

 directly enter them. It occurred to me, however, that I should be more 

 successful if I were to examine every plant noticed with the lip drawn back 

 against the column. Acting on this idea I soon found three, each inclosing a 

 small dipterous insect. Two of these had no traces of pollen on them, and 

 the flowers were not fertilized. The third was dead, apparently not having 

 been able to find the passage out of its prison. It had the remains of two 

 pollinia attached to its back. The stigma of the flower was also plentifully 

 covered with pollen, which had evidently been conveyed from another plant, 

 for all four pollen-masses were intact and undisturbed in their cells. 



' The fact of this insect being unable to effect its escape led me to examine 

 a considerable number of flowers which had commenced to wither, and in 

 which the sepals and petals had closed together, with the view of ascertaining 

 if this circumstance was of frequent occurrence. The results were important. 

 Out of 110 specimens examined seventeen contained dead insects, and nine of 

 these insects bore traces of having had pollen attached to them. Some had 

 followed the passage between the wings of the column until they had reached 

 the anther, and then becoming glued to the pollen-masses had not been able to 

 drag them out of their cells, thus perishing on the threshold of their prison. 

 Many of the flowers which did not inclose insects exhibited signs, besides 

 the removal of the pollinia, of having been visited by them, from the presence 

 of hairs, etc., adhering to the stigma and rostellum; and in one instance the 

 antenna of some insect was found glued to the rostellum, proving that its 

 owner had escaped by crawling through the passage in front of that organ. 



All the insects jjroved to be Diptera, and all are probably referable to one 

 species. I am not, however, entomologist enough to be able to indicate its 

 name. What inducement there is to visit the plants I cannot conjecture, for 

 even with the most careful examination I have not been able to detect the 

 presence of any nectar, or nectar-secreting organs. 



The comparatively large number of insects retained in the flowers examined 

 appears at first sight to show a serious imperfection in the contrivances for 

 insuring fertilization, as it is evident that it is a loss to the plant when its 

 visitor cannot escape and carry away the pollinia. On a closer examination, 

 however, it probably only proves how carefully the passage for the exit of the 



