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STUDIES IN THE CALENDULEAE
489
or iucurved, smooth or furnished with all kinds of slructures ön the
surface, such as furrows and ridges, wings and processes of varying
sluipe. Fortunately, most of the species have homomorphous ray
achenes, which grcatly facililates the taxonomical arrangemenl in the tribe.
Several, however, have dimorphous or Irimorphous ray achenes and a
few have polymorphous achenes. The |alter, in parlicular, have
com-plicated the delimilation of the genera and species.
A common type of ray achene is the trilateral or triangular one with
one primarv nerve in each angle (Lanza 1919, lab. I, fig. 14). It occurs
most markedly in Dimorphotheca and certain sections of
Osteospermum. In transvcrse section these achenes are in many species möre or
less distinctly cuneiform with the acute angle directed towards Ihe
centre of Ihe head. Their tangential side is liormally somevvhat convex
and Iheir radial sides are möre or less plane. As the ray achenes are
arranged in a circle in the periphery of the lieads, their construction is,
of course, the most practical from the point of view of Organization, al
leasl in cases where the heads have numerous ray florets and where
Ihesc are tightlv packed against each other.
From the trilateral type it is cpiite easy to derive most of the other
achene types in the tribe. As I have not vet published the chapter
dealing with the anatomy of the fruits of the tribe Calendiileae, 1 shall
here confine myself to giving a survev of the outward form and
con-sistence of the ray fruits in so far as it can be of interest in iiidicating
interrelation and evolution in the tribe.
The angles of the trilateral achenes, each of which is provided
with a primarv nerve, are blunt or sharp (I p. 239, fig. 23 c) or expanded
into wings (1 p. 67, fig. 4j; p. 205, figs. 19 a, f). Most of the species
have only one of these three achene types in their heads and Ihen the
characters of the achenes have a relatively high taxonomic value.
However, in the heterocarpous species two or three of them may occur in
one and the same head, e.g. Osteospermum rigidum (1, p. 199, fig. 18),
and the achene form is Ihen, of course, of secondary importance.
In the Calenduleae there is a continuous series of intermediate
forms between bluntly and sh:irplv triangular and Ibree-winged achenes.
Derivation of the Ibree-winged achenes from the bluntly triangular
achenes is thus quite simple.
What is particularly interesting is the pronounced helerocarpism
in certain species. In one and the same head achenes of primitive type,
e.g. bluntly triangular, develop in a number of ray florets and in other
ray florets achenes of niuch advanced type, e.g. broadly Ibree-winged,
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