152 VANDE^. Chap. VI 



and until stretched are rarely visible, for the pollen- 

 masses lie close to the pedicel of the rostellum. These 

 caudicles answer both in position and function to the 

 elastic threads, by which the packets of pollen are tied 

 together in the Ophreae, at the point where they become 

 confluent ; for the function of the true caudicle in the 

 Vandeae is to break when the masses of pollen, trans- 

 ported by insects, adhere to the stigmatic surface. 



In many Vandeae the caudicles are easily ruptured, 

 and the fertilisation of the flower, as far as this point 

 is concerned, is a simple affair ; but in other cases their 

 strength, and the length to which they can be stretched 

 before they break, are surprising. I was at first per- 

 plexed to understand what purpose these qualities 

 could serve. The explanation probably is that the 

 pollen-masses in this tribe are very precious objects ; 

 in most of the genera a flower produces only two, and 

 judging from the size of the stigma both are generally 

 left adhering to it. In other genera, however, the 

 orifice leading into the stigma is so small that probably 

 only one pollen-mass is left on it, and in this case the 

 pollen from one flower would suffice to fertilise two 

 flowers, but never a greater number. From the large 

 size of the flowers of many of the Vandeae, they no 

 doubt are fertilised by large insects, and these whilst 

 flying about would be likely to brush away and lose 

 the pollinia attached to them, unless the caudicles were 

 very strong and highly elastic. So again, when an 

 insect thus provided visited a flower either too young, 

 with its stigma not yet sufficiently adhesive, or one 

 already impregnated, with its stigma beginning to dry, 

 the strength of the caudicle would prevent the pollen- 

 masses from being uselessly removed and lost. 



Although the stigmatic surface is astonishingly 

 adhesive at the proper period in many of these Orchids, 



