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490
TYCHO NOR LINDH
are produced. The morphologically most advanced achenes ia
hetero-carpous species determine Ihe taxonomic position of the species.
Terete achenes occur most frequently in species belonging lo llie
genus Osteospermum. The ripe achenes in seven of Ihe species in seel.
Uomocarpa of Osteospermum are distinctly terete and smooth or
slightlv striate (I |). 127. fig. 7), ]nil in these one cail sometimes detect
a trace of three longitudinal ridges.
Even the terete achenes may have prominent blunt or acute ribs
(ridges) or wings. In sect. Polyyaliim of Osteospermum there is a series
of achenes with all these forms represented (I p. 145, fig. 10). Taking
O. polyyaloides’ achenes with three blunt primary ridges (nerves) and
six sccondary ridges as the primitive type, it is easy to derive the achene
form of the other species in this natural section: C). imbricatum by Ihe
primary ridges being acute or narrowlv winged, O. rotundifolium by
reduction of the secondarv ridges and O. corymbosum by reduction of
bolli primary and secondary ridges, it Ihus being quite smooth or
occasionally with a slight suggestion of primary ridges.
In the series of fruit forms in the |ribe Calenduleae all the
transi-tional s|äges are found between terete and trilateral achenes.
The ray achene is not alwavs provided with entire angles and
entire wings. A number of species have instead achenes with cremte
angles (I p. (57, fig. 4 d) or with angles divided into a line of processes
of differing shape and size, e.g. prickle-like (aculeate) processes (I p.
182, figs. 17 a, c, d, f, g, b) and winged processes (I p. (57, fig. 4a).
These achenes with prickle-like or winged processes are easily derived
from simple Irilaleral achenes bearing crenate angles, for a fairly
con-tiniioiis series of intermediate forms links these extremes. The achenes
with winged processes sliould not be confused with achenes bearing
lacerate wings, for in these the wings are entire riglit to the maturity
of Ihe fruit. Through tension in Ihe tissues the wings Iben splil up Inni
the margin in towards Ihe point of attachment into a varying number
of laciniae (I p. 229, lig. 22 d). In achenes furnished with winged
processes no such ruplure has taken place, the processes being independenl
of each other from an early stage in Ihe development of the achenes.
Three-winged achenes are of no taxonoinical vallie in the
definition of genera hut are in certain cases iinportaiit for the distinction of
sections, e.g. seel. Trialata of Osteospermum. They occur in
Dimorpho-theca, Calendula and bolh subgenera of Osteospermum. In the lieads
of niaiiy species they appear in varying number togetlier with achenes
of another type.
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