182 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VH 



which the lip became converted first into the lower mandible of an 

 avicularium and then into an elongated bristle, likewise served as 

 a protection in different ways and under different circumstances. 



In the vegetable kingdom Mr. Mivart only alludes to two cases, 

 namely the structure of the flowers of orchids, and the movements 

 of climbing plants. With respect to the former, he says, " the 

 explanation of their origin is deemed throughly unsatisfactory 

 utterly insufficient 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 pollinia. A pollinium when highly developed consists of a 

 mass of pollen-grains, affixed 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 considered ; yet I may mention that at the base of the 

 orchidaceous 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 considerable length and highly developed, 

 we have good evidence in the aborted pollen-grains which can some- 

 times be detected embedded within the central and solid 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 belonging to other orders the stigma 

 secretes a little viscid matte/. Now in certain orchids similar 

 viscid matter is secreted, but in much larger quantities by one 

 alone of the three stigmas ; and this stigma, perhaps in conse- 

 quence of the copious secretion, is rendered sterile. When an 

 insect visits a flower of this kind, it rubs off some of the viscid 

 matter and thus at the same time drags away some of the pollen- 

 grains. From this simple condition, which differs but little from 

 that of a multitude of common flowers, there are endless 

 gradations, to species in which the pollen-mass terminates in 

 a very short, free caudicle, to others in which the caudicle 

 becomes firmly attached to the viscid matter, with the sterile 

 stigma itself much modified. In this latter case we have a 

 pollinium in its most highly developed and perfect condition. He 

 "/ho will carefully examine the flowers of orchids for himself will 



