YALUE OF CHARACTERS. 353 
flattened, are often dorsally so, or, if the inner edge protrudes, they 
become triquetrous. 
In longitudinal development the achene is either equally grown 
at both ends, so as (if terete) to form a regular eylinder, or tapers 
at the upper end beyond the seed into what was formerly called a 
stipes to the pappus, but is now recognized as a neck or beak to 
the achene, or tapers at the lower end into more or less of a stipes, 
all which forms variously combined, being readily observed (if ripe 
achenes are obtained ), have been made great use of in the fixation 
of genera or even of subtribes, especially in Cichoriacez ; but one 
of the most prominent differences, between the achene merely con- 
tracted at the top, and the distinctly beaked achene, has now been 
generally abandoned in such genera as Crepis, Leontodon, &c., 
where there occurs every grade from the one to the other; and in 
many genera, of which it is still the most marked character, it is 
necessary to be very cautious in its use. 
The development of the ribs of the achene would at first sight 
seem to hold the same position in the classification of Composite as 
in that of Umbelliferz, the ribs being precisely of the same nature ; 
they represent the ribs or nerves of the calycine leaves which form 
the adnate calyx-tube; their systematic value, however, is more 
varied in Composite than in Umbellifere. These ribs are equal to 
the number of the calycine leaves (usually 5, or sometimes 4) when 
the primary nerve alone or midrib of each leaf is prominent, double 
that number when an intermediate rib is formed between each two 
by the combination of the lateral nerves of each two adjoining 
calyeine leaves, three times (15-12) if these lateral nerves are 
separately developed, four or more times if four or more parallel 
veins are developed from each leaf. This distinction between the 
development and non-development of the secondary ribs has been 
found constant, as far as hitherto observed, for the separation of 
the two principal subtribes of Eupatoriacez, but has quite failed, 
even for genera, in Vernoniacez. In other cases the reduction of 
the ribs to the two marginal ones of flattened achenes, the pro- 
trusion of one, two, three, or more of the primary ribs into acute 
angles, or their expansion into wings, or their regular equidistance, 
or the contraction of some of the intervals between them, are often 
the characters of good genera, but have in many instances (as in 
Chrysanthemum) been too much relied upon, producing generic 
combinations or disseverances far from natural. 
The consistence of the ripe achene is occasionally, but rarely, 
2p2 
