316 THE FERTILISATION OF FLOWERS. [PART JIT. 
which, singly, or in some degree combined, we have become 3 
acquainted with in other families, but never in such happy com-_ 
bination as in the Composite. The following points deserve 
special mention: (1) the close association of many flowers; (2) the - 
accessibility of the honey, as well as its plentiful secretion and 
its security from rain; (3) the possession of a pollen-mechanism, 
which renders ovoss-fertilisation certain in the event of insect- 
visits. | 
1. The association of many flowers in one head is advantageous, — 
for the following reasons: ' 
(a) The flowers are rendered much more conspicuous, and are 
accordingly more visited by insects. Conspicuousness is in most 
cases increased still further either by the florets being directed 
outwards (Cynaroidee), or by the limb of the corolla developing 
into a long lobe directed outwards, both of which phenomena 
become more marked towards the margin of the capitulum; 
or by the marginal florets becoming large coloured radiating ” 
laminz, at the expense of the stamens or of both stamens and 
pistil (Asteroidec) ; or, finally, by the innermost bracts performing 
this function (Carlina). q 
(b) Insects can fertilise numerous flowers with much less loss” 
of time than when the flowers are separate; and so the chance — 
of being fertilised is increased for every flower in the same ratio. 
The florets of the disk usually constitute a flat surface over which 
the insect crawls, and from which the reproductive organs protrude — 
far enough to permit simultaneous fertilisation of many florets. 
(c) As the involucre of the whole capitulum plays the part 
of a calyx in protecting the flowers, the calyces of the separate 
florets can be dispensed with entirely, or they may be adapted 
for a new and important purpose by being transfotmed into _ 
structures which aid the dispersion of the seeds by the wind, or 
into barbs furnished with recurved hooks (Bidens), which aid the 
transport of the seeds by animals. 
2. The free accessibility of the honey is a character which 
most Compositee share with Umbelliferze ; and, accordingly, the two 
orders rival one another in the variety of their insect-visitors (vide 
Cirsium arvensis). But while in Umbelliferze the honey lies fully — 
exposed to the rain upon the fleshy disk which secretes it, im 
Composite it is secreted by a ring surrounding the style at the | 
base of a narrow tubular corolla, and as it accumulates it rises up 
into the wider part of the corolla where it is accessible to the most 
short-lipped insects, and where the anthers shelter it from rain. 
