304: MISCELLANEOUS OBJECTIONS TO THE [Chap. VII. 



orchids, and the movements of climbing plants. With 

 respect to the former, he says, " the explanation of their 

 origin is deemed thoroughly unsatisfactory — utterly in- 

 sufficient to explain the incipient, infinitesimal begin- 

 nings of structures which are of utility only when they 

 are considerably developed." As I have fully treated 

 this subject in another work, I will here give only a few 

 details on one alone of the most striking peculiarities of 

 the flowers of orchids, namely their poUinia. A pollin- 

 ium when highly developed consists of a mass of pollen- 

 grains, aifixed to an elastic foot-stalk or caudicle, and 

 this to a little mass of extremely viscid matter. The 

 pollinia are by this means transported by insects from 

 one flower to the stigma of another. In some orchids 

 there is no caudicle to the pollen-masses, and the grains 

 are merely tied together by fine threads; but as these 

 are not confined to orchids, they need not here be con- 

 sidered; yet I may mention that at the base of the or- 

 chidaceous series, in Cypripedium, we can see how the 

 threads were probably first developed. In other orchids 

 the threads cohere at one end of the pollen-masses; and 

 this forms the first or nascent trace of a caudicle. That 

 this is the origin of the caudicle, even when of con- 

 siderable length and highly developed, we have good 

 evidence in the aborted pollen-grains which can some- 

 times be detected embedded within the central and 

 soUd parts. 



With respect to the second chief peculiarity, namely 

 the little mass of viscid matter attached to the end of 

 the caudicle, a long series of gradations can be specified, 

 each of plain service to the plant. In most flowers be- 

 longing to other orders the stigma secretes a little viscid 

 matter. Now in certain orchids similar viscid matter 



