54 



of the sticky stigma, so as to press it back against the pollen- 

 masses (see g, in text figure). So accurate is the apposition 

 that even the horizontal groove (m) at the back of the gland 

 finds a corresponding ridge (n) at the base of the stigma, which 

 exactly fits into it. 



The margins of the dorsal sepal now curl inwards and 

 envelope the edges of the labellum. The flower has returned 

 to its second childhood — the bud condition — and the whole of 

 the sexual apparatus is shut off and sealed against external 

 influences. 



It is this effectual sealing up which I believe to be the 

 important function of the labellum and its gland. Orthoceras 

 blooms during extremely hot weather, December and January, 

 when conditions are dry and arid. It would seem desirable 

 that the sexual parts should be kept moist until fertilization 

 has become definitely effected, a period of probably about three 

 weeks in this species. 



Prasophyllum gracile, Rogers. PI. vii.A. 



The discovery of a new locality where this hitherto rare 

 orchid grows in great abundance, has afforded me the oppor- 

 tunity of carefully studying its mode of pollination. 



The anther-case is about the same length as the column, 

 reaching to the level of the rostellum. In the immature flower 

 it completely covers the two pollinia and the caudicle, which 

 at this stage lie closely in contact with the back of the stigma 

 and rostellum. A strap-like caudicle attaches the pollinia to 

 a somewhat triangular disc in the manner shown in fig. 6 of 

 pi. vii.A. The rostellum fits into the wedge-shaped space 

 between the caudicle and disc, receiving the latter into a 

 slot-like depression on its anterior surface. The lateral 

 appendages of the column are somewhat shorter than the ros- 

 tellum, and protect the stigma on each side. The latter is 

 voluminous and sticky. 



The disc with attached pollen-masses can be easily removed 

 from the rostellum by an upward shearing force. It is sticky 

 on its rostellar side, and adheres to the object removing it. 

 After remxoval the pollinia rotate through an angle of about 

 180°. 



The flowers are much frequented by a small beetle, 

 Trogoderma adelaidcE, and in several instances I found 

 pollinia adhering to the cephalo-thorax of these insects and 

 presenting forward in such a position that they must have been 

 deposited on the stigma of a flower had the carrier attempted 

 to crawl towards the base of the labellum, a locality which 

 they appear to frequently visit. 



