544 THE FERTILISATION OF FLOWERS. [PART III. 
in length to be able to reach the honey through these passages, 
and one of at least double that length to drain one of these spaces 
of its honey. Each foliar division of the style bears on its under 
surface near its apex a scale-like process, whose upper surface is 
the true stigma. Hence insects touch the stigma with their backs 
only when creeping in under the petaloid style; for as they creep 
out again they push the papillar surface upwards. Close under 
the petaloid styles lie the three anthers, whose pollen-covered 
surfaces are directed downwards. Self-fertilisation is thus rendered 
impossible. 
Fig. 181.—Iris Pseud-acorus, L. 
1.—Transverse section through the tubular part of the perianth. 
2.—Transverse section through the petianth, at the point where its six segments become free. 
3.—Transverse section somewhat higher than 2, to show the relation of the three pairs of nectaries 
to the divisions of the style and the outer segments of the perianth. 
a, style ; a’ a’ a’, the three foliaceous divisions of the style ; b, honey receptacle ; ¢ ec, lower part 
of filaments, adherent to the outer segments of the | pigs ddd; ddd, inner segments of the 
perianth ; ee, the tworidges on each outer segment of the perianth, which, together with the bases of 
the filaments, bound the entrance to the nectary. 
Sprengel,! has given a very full account, with figures, of the 
flowers of Jris Pseudacorus and J. Xiphium. His observations of 
insect-visitors were, however, not nearly sufficient, and his 
conception of the mode of fertilisation must be modified. 
In Sprengel’s opinion, both species of Iris are fertilised exclusively 
by humble-bees. A bee alights on one of the large outer segments of 
the perianth, toward the base of which it pushes its way under the 
over-hanging petaloid style, until it reaches the entrances to the two 
nectaries. After it has sucked the honey it crawls backwards to its 
starting-point, and then flies to the second outer perianth-segment, 
where it performs the same operation ; thence to the third, thence to 
another flower, and so on. On entering the flower, the back of 
the bee rubs the upper surface of the scale projecting from the 
d Sprengel, No, 702, pp. 69-78, Plate II. 
