Cheeseman. — On the Fertilisation of Acianthus and Cyrtostilis. 349 



Art. L. — On the Fertilisation of Acianthus and Cyrtostilis. 

 By Thomas F. Cheeseman, F.L.S. 



[Read before the Auckland Institute, 1st June, 1874.] 



1. Acianthus sinclairii. 



In examining the fertilisation of this plant, we do not find contrivances 

 so remarkable and unique as those that obtain in Pterostylis, or in other of 

 tbe New Zealand Orchids j on the contrary, the mode employed is simple, and 

 presents few features of interest. Yet, if the completeness of any method of 

 fertilisation is to be judged of by the results obtained, as undoubtedly it 

 should be, we must regard that of Aciaoithus as one of the most perfect of the 

 many different modes in use among our Orchids. 



The flowers, varying in n amber from one to twelve, are minute, and of an 

 inconspicuous appearance. The lip, which is horizontally spread out in front 

 of the flower, or slightly deflexed, is ovate-lanceolate in outline, and greatly 

 concave, so as to form a kind of bucket. At its base it is furnished with two 

 large glands, and the margins and point are also plentifully studded with 

 minute fleshy papillae. The column is somewhat curiously shaped. At first it 

 is erect, but towards the summit suddenly arches over the lip, and is much 

 thickened and expanded. The anther is terminal, two-celled, each cell 

 possessing two pollinia, which are deeply bilobed, so as to resemble a horse 

 shoe in shape. The stigma is a deep circular hollow situated just below the 

 anther ; and, by the arching of the upper part of the column, hangs directly 

 over the lip. The rostellum is placed on its upper margin. It consists of two 

 triangular projections, which at first are cellular, but ultimately resolve into 

 masses of viscid matter, covered with an extremely delicate membrane. As 

 the flower expands, the connection of these projections with the rest of the 

 column becomes very slender, so that at last they can be detached by a 

 comparatively slight touch, leaving the upper margin of the stigmatic chamber 

 quite plane. 



Long before the flower opens, each lobe of the anther splits gradually from 

 base to apex, allowing the included pollinia almost to touch the upper part of 

 the rostellate points. The pollinia then emit a number of excessively delicate 

 thread-like projections, which reach the rostellum, and become firmly attached 

 to it. So that, in a fully expanded flower, each set of pollen-masses is quite 

 free from its anther cells, but they are firmly attached by their bases to their 

 respective rostella, neither of which can be removed without bringing away 

 the pollinia. 



The glands at the base of the lip secrete nectar, which is stored up in the 

 cavity just in front of them. Erom this circumstance alone we might surmise 



