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Tubercle Development in Mammillaria heyderi

Norman H. Boke
American Journal of Botany
Vol. 40, No. 4 (Apr., 1953), pp. 239-247
Stable URL: http://www.jstor.org/stable/2438661
Page Count: 9
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Tubercle Development in Mammillaria heyderi
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Abstract

Mammillaria heyderi is a laticiferous member of the subtribe Coryphanthanae. Its shoot apex reaches a maximum diameter of about 1500u, the largest yet described for any flowering plant. The leaves attain a length of less than 50u and are the most rudimentary ones yet reported for any cactus. M. heyderi possesses what may be called dimorphic areoles. The meristem of the spine-producing areole arises first and is soon elevated to the apex of the tubercle. As in Coryphantha, the tubercle is a much-enlarged leaf base. The first spine to be initiated is abaxial to the areole meristem. Subsequent spine primordia arise around either side of the areole meristem until a complete ring of primordia has been formed. The usually solitary central s pin, is the last to be initiated. Most of the areole meristem is used up in the initiation of the central spine, and what remains soon becomes indistinguishable from adjacent parenchyma. The spine areole of M. heyderi has a radial aspect unusual among investigated members of the Cereeae. Floral primordia are initiated in the axils of some of the tubercles after the spine areoles have been elevated to the top. The flowering areole produces trichomes, a series of lateral appendages homologous with spines, and eventually a single flower. The flowering areole is interpreted as comparable to the serial or supernumerary buds found in many other plants. Histogenetic evidence does not permit the interpretation of spine areole and flowering areole as having arisen ontogenetically by division of a single areole meristem.

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