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492
TYCHO NOR LINDH
achenes of quite a different type. The number of rostrate achenes is
small, there being usually 1—3 in eacli head.
The evolution of drupes is extremelv rare in the Compositae. The
small genus Chry sant hemoides represen ts such a line of development
in the tribe Calenduleae (I p. 376, fig. 41). This genus has its centre in
South Africa and is most easily derived from Osteospermum, the outer
pericarp of the achenes not becoming hardened but fleshy and edible.
There are certain morphological similarities between the species in
Chrysanthemoides and sect. Coriacea of Osteospermum, especially as
regards the leaf type. Drupes are also found in the South American
genera Wulffia Neck, and Clibadium L., which belong to the tribe
Helianthoideae of the Compositae. As far as is known at present, no
other plants in this family have drupes. These fruits may also be
designated as drupaceous cypsela, because the sarcocarp in its
morphological origin is partly derived from the adnate receptacle tube.
The main types of fruits that have now been discussed, are mel
with in the South African species of the tribe Calenduleae. Most of
these species are, as we know, homomorphous or only very slightly
heteromorphous in respect of the fruit form, only a small number of
them having reallv heteromorphous achenes.
All the Mediterranean species belonging to the tribe, ön the other
hand, have markedlv heteromorphous achenes. Calendula has two of
the above-mentioned achene types in common with the South African
species, namely the 3-winged type (Lanza, 1919, tab. II, fig. 84; lab.
IV, figs. 5 d and e, etc.) and the rostrate type (op. cit., tab. IX, fig. 1 d;
tab. X, fig. 2 b, etc.).
Lanza dislinguished four main types of achenes in Calendula, viz.
1. annulate (= vermiformi), 2. cymbiform ( = naviculari), 3.
three-winged and 4. rostrate. Three of these types frequently occur in one and
the same head.
In the Calendula species type 1, i.e. the annulate achene, is
always produced in each capitulum. !l is solely Ihe presence of such
achenes that cail motivate the separation of this genus from
Osteospermum. This type of achene must be regarded as strongly advanced and
as having evolved through a gradual incurvature of the inner ray
achenes. A fairly continuous series of intermediate forms between
almost straight and annulately incurved achenes in Ihe heads of
Calendula reflects the progress of the evolution.
In some Osteospermum species (I p. 179, fig. 16 a: p. 348, fig. 36 a)
one can Irace a distinct tendency towards incurvation of the achenes.
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