854 MR. G. BENTHAM ON COMPOSIT X. 
useful as a generic character. The thick achene, whether hard 
and bony or fleshy, is only to be met with in Cynaroidez, Arcto- 
tides, Calendulacee (Osteospermum), and a few Helianthoidee ; 
but even there, although pretty constant in genera, is unavailable 
for tribualor even subtribual distinctions. The pericarp is never, 
I believe, truly crustaceous and fragile, but from the ordinary con- 
sistence it passes in a few genera into thinly membranous. The 
smooth pitted or muricate surface has been made use of in the 
case of some Cichoriacee especially, but cannot be implicitly relied 
on. In some genera of Helianthoidez, for instance, as also in 
Villanova, Adenostemma, Brachycome, and some others, strongly 
muricate and perfectly smooth achenes are met with in different 
capitula of the same specimen, or proceeding from different florets 
of one and the same capitulum. The difference between the 
densely silky-hairy and the glabrous or slightly hirsute achene, 
and in some cases the woolly indumentum, has been found a good 
generic character in some Helenioides, Cynaroides, Arctotide:e, 
Mutisiaceee, and Cichoriacee. 
The pappus may be best considered under the head of the fruit ; 
for although homologically it is generally admitted to be an altered 
or semiabortive calyx-limb, and although when present it is always 
already to be met with at the time of flowering, yet it is on the 
ripe achene that it has attained its fullest development in those 
innumerable variations which strike the eye of the most super- 
ficial observer, and which have been eagerly seized upon to cha- 
racterize a large proportion of the thousand and one petty genera 
with which synantherology has been encumbered. Constant or 
nearly so in each species, with very few exceptions, the pappus 
will often, in a most natural genus, so vary from species to species, 
as to make it a most difficult task to decide whether it should be 
neglected altogether, or, if taken into account, what modifications 
may be taken as generic, subtribual, or tribual. 
The presence or absence of a pappus or its degree of develop- 
ment is always of much less importance than its nature when 
present ; for there are frequently exceptional species or varieties- 
where it is wanting in genera or species where it is usually present ; 
and therefore it is, that where we have a specimen with no pappus, 
we must be very careful to determine its affinities by other cha- 
racters. In some cases, however, the absence of pappus has 
proved a really constant generic character, and is often a clue 
at least to the tribe of a Composite. It is, for instance, almost 
