Christoph Oberprieler The Systematics of Anthemis L. - Herbmedit.org

Bocconea 9 - 1998 35
ribbed, the large sc1ereids are found on top of and/or along the sides of the internaI ribs of
the fibre cell layer, accentuating the external ribs and their sculpturing with tuberc1es.
However, achenes of A. arvensis and related species of A. ser. Anthemis display a quite
differently patterned mesocarp: The inner cylinder of libriform fibre cells is conspicuously
ribbed, as in all other species of A. sect. Anthemis, but the external ribs of the achene are
placed on top of the internaI furrows. This is caused by a parenchymatous outer mesocarpic
layer of cells that divide intensively during maturation. Since the parenchyma is thicker
above the internaI furrows of the sc1erenchymatic cylinder than above its ribs, the latter
will eventually coincide with the furrows of the achene.
From peripheral disc achenes to centraI ones, one may note a trend to reduction of
sc1erenchymatic mesocarp tissue. This trend is particularly obvious in some representatives
of Anthemis ser. Chrysanthae and ser. Bourgaeinianae. Unlike other taxa in
A. sect. Chrysanthae, A. tenuisecta subsp. tenuisecta has achenes that usually lack a continuous
layer of sc1erenchymatic mesocarp tissue. Libriform fibre cells are confined to
bundles in the ribs, and the outer mesocarpic cell layer remains parenchymatous. Same is
true for all achenes of A. monilicostata and the centraI achenes of A. stiparum and
A. mauritiana of A. sect. Bourgaeinianae.
The cells of the endocarp remai n parenchymatous and soon become compressed during
achene maturation. In ripe achenes they cannot usually be identified. The testa consists of
an epiderrnis and 2-3 layers of large, parenchymatous cells that soon disintegrate during
maturity. Cells of the testa epiderrnis are characterised by curved and conspicuously thickened
radiai walls. The testa epiderrnis and the endosperm layer surrounding the cotyledons
are still visible in mature achenes.
lO. Chromosomes
Material and methods
Far the study of pollen mother cell (PMC) meiosis, buds of capitula were fixed in 96 %
ethanol/glacial acetic acid (3 : l) in the field and stored in a refrigerator after return to
Berlin. For chromosome staining several buds of disc florets were removed from the capitula,
coarsely crushed, and squashed in aceto-orcein.
For the study of rnitosis, root tips were obtained either by growing plants in the Botanic
Garden Berlin~Dahlem or by gerrninating achenes in petri dishes. In both cases root tip
meristems were pre-treated with hydroxyquinoline (0.002 molar aqueous solution) for 4
hours, fixed in 96 % ethanol/glacial acetic acid (3 : l) and refrigerated. Hydrolysis was
performed with 1-2n hydrochloric acid for lO rninutes at 60°C. For chromosome staining
root tips were squashed in aceto-orcein.
Camera lucida drawings of chromosomes were made with a Zeiss Standard 16 rnicroscope
and measured with an ocular rnicrometer of a Wild M5A stereornicroscope for arm
lengths. The PC program CHROMEX described by Voss & al. (1994) was used to transfer
measurements to a karyological database, to sort chromosomes automatically according to
their length and arm ratios, to find homologous chromosomes interactively, to construct
idiograms, and to calculate means of multiple probes. For the description of karyotypes the