VALUE OF CHARACTERS. 355 
always present in Senecionide, and very frequently deficient in 
Anthemides. There is not, however, a single tribe in which there 
is not at least one genus deprived of all pappus. 
Among the various peculiarities by which the pappus is diver- 
sified, it is a very difficult question to determine which are and which 
are not of importance in classification, whether we reason à priori 
from the presumed homology and functions of the organ, or 
whether we confine ourselves to the experience of its conformity 
or non-conformity to variations of other organs. Asa general rule, 
the greater the consolidation and contraction of the inner and 
more important floral organs, and the more the outer compara- 
tively vegetative organs are called in to assist in some part of the 
reproduetive functions, the more constant and important in 
classification are the latter. In Composite we have alluded to 
the great condensation of the floral organs; and, amongst other 
reduetions, the calyx-limb, in the form of a pappus, appears to 
have its functions annihilated or confined to the sole purpose of 
assisting in the dissemination of the seed, whilst its ordinary part 
of protecting the young flower is here supplied by the bracts 
collected in an involucre. The modifications under which this 
pappus is acted on by wind, or adheres to extraneous substances, 
ought therefore to be systematically important, as well as those 
which are indications of its homologies. On the other hand, the 
pappus being in so many cases a very much reduced or rudimén- 
tary organ, those differences depending on the degree of develop- 
ment must, as in the case of other rudimentary organs, be very 
little relied on. T 
Of these modifications, we may first consider the indications of 
homologies. If the pappus is a reduced calyx-limb, then in all 
cases where it consists of a single ring of bristles or palex it is 
easy to suppose that these may represent the parallel ,veins, 
nerves, or ribs of the calyx-lobes or calycine leaves—more especi- 
ally as they, or at least the most valid among their number, often 
correspond in number, and are even in direct continuation of the 
ribs of the achene ; but where these bristles are very numerous 
and crowded in a dense tuft, scarcely separable into series, or 
where they form several concentric series, very distinct from each 
other and often differing in nature, their homology is not so easy 
to settle. Most probably the longest or principal series repre- 
sent the calyx-ribs, which may sometimes, owing to their great 
number and crowded state, become forced, as it were, into two or 
