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Areole Histogenesis in Mammillaria lasiacantha

Norman H. Boke
American Journal of Botany
Vol. 45, No. 6 (Jun., 1958), pp. 473-479
Stable URL: http://www.jstor.org/stable/2439183
Page Count: 7
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Areole Histogenesis in Mammillaria lasiacantha
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Abstract

Mammillaria lasiacantha has spiniferous meristems at the apices of its tubercles and floral, or vegetative, meristems in the axils. The vegetative meristems will form lateral branches if the parent shoot apex is destroyed. Spiniferous and axillary meristems are interpreted as serial buds, although they appear to be formed by division of a common meristem. The division occurs after spine initiation has begun, and while the axillary portion is still confluent with the shoot apex. Although the axillary meristem is more precocious than in certain other species, its mode of origin is essentially the same. Arguments as to whether axillary meristems in the mammillarias arise by division of a common meristem or whether they arise somewhat later from cells left behind in the axils of the tubercles, now appear academic. The first spine primordium on a tubercle of M. lasiacantha appears immediately in front of the rudimentary leaf. Other spines are initiated in several elliptical series, each of which eventually surrounds the spiniferous meristem. The last spine primordia form in the center of the areole, and the spiniferous meristem is "used up" in the process. The spines elongate in basipetal sequence, beginning at the forward side of the tubercle. While M. lasiacantha has no mucilage-bearing idioblasts, there are regions in the outer cortex which exude a translucent substance when fresh specimens are cut. These are not laticifers of the type found in other mammillarias. Mammillaria lasiacantha has a relatively wide pith, but no medullary vascular system. The results of the study offer little help in deciding whether Buxbaum's recent proposal to separate this and related species into a new genus, Ebnerella, is justified. At least, they do not strongly support it.

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