REVIEWS. 
177 
plundering the nectary of one flower, flies away to visit another, it will 
insert the pollinium or pollinia that it may have extracted from the first 
into the corresponding part of the second, and, as Mr. Darwin remarks, the 
attached pollinium would simply he pushed into its old position, entirely 
avoiding the stigma, which is situated immediately below. To get over this 
difficulty one of the most remarkable “ contrivances ” of the whole series 
comes into play. It is described as follows by Mr. Darwin : — “ Though the 
viscid surface,” he says, u remains immovably affixed, the apparently insig- 
nificant and minute disc of membrane to which the caudicle adheres is 
endowed with a remarkable power of contraction, which causes the polli- 
nium to sweep through an angle of about ninety degrees, always in one 
direction, viz., towards the apex of the proboscis or pencil, in the course of 
thirty seconds on an average. The position of the pollinium after the 
movement is shown at n in fig. 2. After this movement, completed in an 
Fig. 2. 
A 
POINT OF A PENCIL WITH POLLINIUM OF ORCHIS MASCULA ATTACHED TO IT, 
IN TWO POSITIONS. 
A. The position of the pollen-mass when first attached. 
b. Its position after the act of depression. 
interval of time which would allow an insect to fly to another plant, it will 
be’seen by turning to the diagram (fig. 1, a), that if the pencil be inserted into 
the nectary the thick end of the pollinium now exactly strikes the stigmatic 
surface.” The viscidity of the surface of the stigma causes the pollinia to 
adhere to it ; but the peculiar composition of the latter, consisting as they do 
of numerous packets of pollen-grains held together only by slender threads,* 
renders the breaking up of the pollinium an easy matter. Hence only a 
small quantity of the pollen-grains remains attached to the stigma, and thus 
a pollinium attached to the head of an insect may be applied successively to 
several stigmas and fertilize them all. Mr. Darwin says that he has often 
seen the remains of the pollinia of another species of Orchis “adhering to the 
proboscis of a moth, with the stump-like caudicles alone left, all the packets of 
pollen having beeD left glued to the stigmas of the successively visited flowers.” 
Of the reality of this process no doubt can be entertained. The actual 
phenomena of the removal of the pollinia may be produced experimentally, 
* It is evidently to the degree of coherence of the pollinia, and not, as 
Mr. Darwin seems to think, to the degree of viscidity of the stigma, that 
the breaking up ot the former is to be ascribed. 
